IBM AIX 7.x Security Technical Implementation Guide

The "/etc/security/mkuser.sys.custom" is called by "/etc/security/mkuser.sys" to customize the new user account when a new user is created, or a user is logging into the system without a home directory. An improper "/etc/security/mkuser.sys.custom" script increases the risk that non-privileged users may obtain elevated privileges. It must not exist unless it is needed.

By limiting the number of failed login attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-force attacks, is reduced. Limits are imposed by locking the account.

Satisfies: SRG-OS-000021-GPOS-00005, SRG-OS-000329-GPOS-00128

Without path validation, an informed trust decision by the relying party cannot be made when presented with any certificate not already explicitly trusted.

To assure accountability and prevent unauthenticated access, organizational users must be identified and authenticated to prevent potential misuse and compromise of the system.

Organizational users include organizational employees or individuals the organization deems to have equivalent status of employees (e.g., contractors). Organizational users (and processes acting on behalf of users) must be uniquely identified and authenticated to all accesses, except for the following:

1) Accesses explicitly identified and documented by the organization. Organizations document specific user actions that can be performed on the information system without identification or authentication; and

2) Accesses that occur through authorized use of group authenticators without individual authentication. Organizations may require unique identification of individuals in group accounts (e.g., shared privilege accounts) or for detailed accountability of individual activity.

To assure accountability and prevent unauthenticated access, organizational users must be identified and authenticated to prevent potential misuse and compromise of the system.

Organizational users include organizational employees or individuals the organization deems to have equivalent status of employees (e.g., contractors). Organizational users (and processes acting on behalf of users) must be uniquely identified and authenticated to all accesses, except for the following:

1) Accesses explicitly identified and documented by the organization. Organizations document specific user actions that can be performed on the information system without identification or authentication; and

2) Accesses that occur through authorized use of group authenticators without individual authentication. Organizations may require unique identification of individuals in group accounts (e.g., shared privilege accounts) or for detailed accountability of individual activity.

A replay attack may enable an unauthorized user to gain access to the operating system. Authentication sessions between the authenticator and the operating system validating the user credentials must not be vulnerable to a replay attack.

An authentication process resists replay attacks if it is impractical to achieve a successful authentication by recording and replaying a previous authentication message.

A privileged account is any information system account with authorizations of a privileged user.

Techniques used to address this include protocols using nonces (e.g., numbers generated for a specific one-time use) or challenges (e.g., TLS, WS_Security). Additional techniques include time-synchronous or challenge-response one-time authenticators.

Satisfies: SRG-OS-000112-GPOS-00057, SRG-OS-000113-GPOS-00058

The "/etc/security/mkuser.sys" script customizes the new user account when a new user is created, or a user is logging into the system without a home directory. An improper "/etc/security/mkuser.sys" script increases the risk that non-privileged users may obtain elevated privileges.

Restricting permissions will protect the files from unauthorized modification.

A user's "ttys" attribute controls from which device(s) the user can authenticate and log in. If the "ttys" attribute is not specified, all terminals can access the user account.

All systems are vulnerable if terminals are left logged in and unattended. Leaving system terminals unsecure poses a potential security hazard.

If the interface is AIXwindows (CDE), use the xlock command to lock the sessions.

If a public directory has the sticky bit set and is not owned by a privileged UID, unauthorized users may be able to modify files created by others. The only authorized public directories are those temporary directories supplied with the system or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system and by users for temporary file storage, (e.g., /tmp), and for directories requiring global read/write access.

To centralize the management of privileged account crontabs, of the default system accounts, only root may have a crontab.

Reserved GIDs are typically used by system software packages. If non-system groups have GIDs in this range, they may conflict with system software, possibly leading to the group having permissions to modify system files.

The library preload list environment variable contains a list of libraries for the dynamic linker to load before loading the libraries required by the binary. If this list contains paths to libraries relative to the current working directory, unintended libraries may be preloaded.

Users' home directories/folders may contain information of a sensitive nature. Non-privileged users should coordinate any sharing of information with an SA through shared resources.

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

The banner must be formatted in accordance with applicable DoD policy. Use the following verbiage for operating systems that can accommodate banners of 1300 characters:

"You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only.

By using this IS (which includes any device attached to this IS), you consent to the following conditions:

-The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations.

-At any time, the USG may inspect and seize data stored on this IS.

-Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose.

-This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy.

-Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details."

Use the following verbiage for operating systems that have severe limitations on the number of characters that can be displayed in the banner:

"I've read & consent to terms in IS user agreem't."

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance.

System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

The banner must be formatted in accordance with applicable DoD policy. Use the following verbiage for operating systems that can accommodate banners of 1300 characters:

"You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only.

By using this IS (which includes any device attached to this IS), you consent to the following conditions:

-The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations.

-At any time, the USG may inspect and seize data stored on this IS.

-Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose.

-This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy.

-Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details."

Use the following verbiage for operating systems that have severe limitations on the number of characters that can be displayed in the banner:

"I've read & consent to terms in IS user agreem't."

While LDAP client's authentication type is ldap_auth (server-side authentication), the client sends password to the server in clear text for authentication. SSL must be used in this case.

A plus (+) in system accounts files causes the system to lookup the specified entry using NIS. If the system is not using NIS, no such entries should exist.

Inaccurate time stamps make it more difficult to correlate events and can lead to an inaccurate analysis. Determining the correct time a particular event occurred on a system is critical when conducting forensic analysis and investigating system events. Sources outside the configured acceptable allowance (drift) may be inaccurate.

Synchronizing internal information system clocks provides uniformity of time stamps for information systems with multiple system clocks and systems connected over a network.

Organizations should consider endpoints that may not have regular access to the authoritative time server (e.g., mobile, teleworking, and tactical endpoints).

Satisfies: SRG-OS-000355-GPOS-00143, SRG-OS-000356-GPOS-00144

Enabling the nosuid mount option prevents the system from granting owner or group-owner privileges to programs with the suid or sgid bit set. If the system does not restrict this access, users with unprivileged access to the local system may be able to acquire privileged access by executing suid or sgid files located on the mounted NFS file system.

A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not log out because of the temporary nature of the absence.

The session lock is implemented at the point where session activity can be determined. The operating system session lock event must include an obfuscation of the display screen so as to prevent other users from reading what was previously displayed.

Publicly viewable images can include static or dynamic images, for example, patterns used with screen savers, photographic images, solid colors, a clock, a battery life indicator, or a blank screen, with the additional caveat that none of the images convey sensitive information.

If LDAP authentication is used, SSL must be used between LDAP clients and the LDAP servers to protect the integrity of remote access sessions.

FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets DoD requirements. This allows for Security Levels 1, 2, 3, or 4 for use on a general purpose computing system.

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. AIX must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated.

OpenSSL FIPS object module is a cryptographic module that is designed to meet the requirements for FIPS 140-2 validation by CMVP and is compatible with OpenSSL libraries. The 2.0.13 FIPS object module version has been FIPS validated and certified by CMVP for multiple AIX versions on Power 7 and Power 8 platforms under certificate #2398.

IBM has released a FIPS capable OpenSSL (Fileset VRMF: 20.13.102.1000), which is OpenSSL 1.0.2j version with 2.0.13 object module. The fileset is available in Web Download Pack.


Satisfies: SRG-OS-000120-GPOS-00061, SRG-OS-000478-GPOS-00223, SRG-OS-000396-GPOS-00176

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

If the operating system allows the user to consecutively reuse extensive portions of passwords, this increases the chances of password compromise by increasing the window of opportunity for attempts at guessing and brute-force attacks.

The number of changed characters refers to the number of changes required with respect to the total number of positions in the current password. In other words, characters may be the same within the two passwords; however, the positions of the like characters must be different.

If the password length is an odd number then number of changed characters must be rounded up. For example, a password length of 15 characters must require the change of at least 8 characters.

Enforcing a minimum password lifetime helps to prevent repeated password changes to defeat the password reuse or history enforcement requirement. If users are allowed to immediately and continually change their password, then the password could be repeatedly changed in a short period of time to defeat the organization's policy regarding password reuse.

The default legacy password hashing algorithm, crypt(), uses only the first 8 characters from the password string, meaning the user's password is truncated to eight characters. If the password is shorter than 8 characters, it is padded with zero bits on the right.

The crypt() is a modified DES algorithm that is vulnerable to brute force password guessing attacks and also to cracking the DES-hashing algorithm by using techniques such as pre-computation.

With the Loadable Password Algorithm (LPA) framework release, AIX implemented a set of LPAs using MD5, SHA2, and Blowfish algorithms. These IBM proprietary password algorithms support a password longer than 8 characters and Unicode characters in passwords.

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity or strength is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor in determining how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Special characters are those characters that are not alphanumeric. Examples include: ~ ! @ # $ % ^ *.

Systems must employ cryptographic hashes for passwords using the SHA-2 family of algorithms or FIPS 140-2 approved successors. The use of unapproved algorithms may result in weak password hashes that are more vulnerable to compromise.

Passwords with excessive repeating characters may be more vulnerable to password-guessing attacks.

The nosuid mount option causes the system to not execute setuid files with owner privileges. This option must be used for mounting any file system not containing approved setuid files. Executing setuid files from untrusted file systems, or file systems not containing approved setuid files, increases the opportunity for unprivileged users to attain unauthorized administrative access.

Without establishing what type of events occurred, it would be difficult to establish, correlate, and investigate the events leading up to an outage or attack.

Audit record content that may be necessary to satisfy this requirement includes, for example, time stamps, source and destination addresses, user/process identifiers, event descriptions, success/fail indications, filenames involved, and access control or flow control rules invoked.

Associating event types with detected events in AIX audit logs provides a means of investigating an attack; recognizing resource utilization or capacity thresholds; or identifying an improperly configured operating system.

Satisfies: SRG-OS-000037-GPOS-00015, SRG-OS-000038-GPOS-00016

Without establishing the source of the event, it is impossible to establish, correlate, and investigate the events leading up to an outage or attack.

Without information that establishes the identity of the subjects (i.e., users or processes acting on behalf of users) associated with the events, security personnel cannot determine responsibility for the potentially harmful event.
In addition to logging where events occur within AIX, AIX must also generate audit records that identify sources of events. Sources of operating system events include, but are not limited to, processes and services.

In order to compile an accurate risk assessment and provide forensic analysis, it is essential for security personnel to know the source of the event.

Satisfies: SRG-OS-000040-GPOS-00018, SRG-OS-000255-GPOS-00096

Reconstruction of harmful events or forensic analysis is not possible if audit records do not contain enough information.

At a minimum, the organization must audit the full-text recording of privileged commands. The organization must maintain audit trails in sufficient detail to reconstruct events to determine the cause and impact of compromise.

The ability to specify the event criteria that are of interest provides the individuals reviewing the logs with the ability to quickly isolate and identify these events without having to review entries that are of little or no consequence to the investigation. Without this capability, forensic investigations are impeded.

Events of interest can be identified by the content of specific audit record fields, including, for example, identities of individuals, event types, event locations, event times, event dates, system resources involved, IP addresses involved, or information objects accessed. Organizations may define audit event criteria to any degree of granularity required, for example, locations selectable by general networking location (e.g., by network or subnetwork) or selectable by specific information system component.

The ability to generate on-demand reports, including after the audit data has been subjected to audit reduction, greatly facilitates the organization's ability to generate incident reports as needed to better handle larger-scale or more complex security incidents.

The ability to perform on-demand audit review and analysis, including after the audit data has been subjected to audit reduction, greatly facilitates the organization's ability to generate incident reports, as needed, to better handle larger-scale or more complex security incidents. If the audit reduction capability does not support after-the-fact investigations, it is difficult to establish, correlate, and investigate the events leading up to an outage or attack, or identify those responses for one. This capability is also required to comply with applicable Federal laws and DoD policies.

Audit reduction is a process that manipulates collected audit information and organizes such information in a summary format that is more meaningful to analysts. The report generation capability provided by the application must support on-demand (i.e., customizable, ad hoc, and as-needed) reports.

This requires operating systems to provide the capability to customize audit record reports based on all available criteria.

Satisfies: SRG-OS-000054-GPOS-00025, SRG-OS-000122-GPOS-00063, SRG-OS-000348-GPOS-00136, SRG-OS-000349-GPOS-00137

Unauthorized disclosure of audit records can reveal system and configuration data to attackers, thus compromising its confidentiality.

Audit information includes all information (e.g., audit records, audit settings, audit reports) needed to successfully audit operating system activity.

Satisfies: SRG-OS-000057-GPOS-00027, SRG-OS-000058-GPOS-00028, SRG-OS-000059-GPOS-00029

Without the capability to generate audit records, it would be difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Audit records can be generated from various components within the information system (e.g., module or policy filter).

The list of audited events is the set of events for which audits are to be generated. This set of events is typically a subset of the list of all events for which the system is capable of generating audit records.

DoD has defined the list of events for which AIX will provide an audit record generation capability as the following:

1) Successful and unsuccessful attempts to access, modify, or delete privileges, security objects, security levels, or categories of information (e.g., classification levels);

2) Access actions, such as successful and unsuccessful login attempts, privileged activities or other system-level access, starting and ending time for user access to the system, concurrent logins from different workstations, successful and unsuccessful accesses to objects, all program initiations, and all direct access to the information system;

3) All account creations, modifications, disabling, and terminations; and

4) All kernel module load, unload, and restart actions.

Satisfies: SRG-OS-000062-GPOS-00031, SRG-OS-000004-GPOS-00004, SRG-OS-000051-GPOS-00024, SRG-OS-000064-GPOS-00033, SRG-OS-000239-GPOS-00089, SRG-OS-000240-GPOS-00090, SRG-OS-000241-GPOS-00091, SRG-OS-000277-GPOS-00107, SRG-OS-000303-GPOS-00120, SRG-OS-000304-GPOS-00121, SRG-OS-000327-GPOS-00127, SRG-OS-000327-GPOS-00127, SRG-OS-000364-GPOS-00151, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000461-GPOS-00205, SRG-OS-000462-GPOS-00206, SRG-OS-000463-GPOS-00207, SRG-OS-000465-GPOS-00209, SRG-OS-000466-GPOS-00210, SRG-OS-000467-GPOS-00211, SRG-OS-000468-GPOS-00212, SRG-OS-000470-GPOS-00214, SRG-OS-000471-GPOS-00215, SRG-OS-000471-GPOS-00216, SRG-OS-000472-GPOS-00217, SRG-OS-000473-GPOS-00218, SRG-OS-000474-GPOS-00219, SRG-OS-000475-GPOS-00220, SRG-OS-000476-GPOS-00221, SRG-OS-000477-GPOS-00222

Protecting audit information also includes identifying and protecting the tools used to view and manipulate log data. Therefore, protecting audit tools is necessary to prevent unauthorized operation on audit information.

Operating systems providing tools to interface with audit information will leverage user permissions and roles identifying the user accessing the tools and the corresponding rights the user enjoys in order to make access decisions regarding the access to audit tools.

Audit tools include, but are not limited to, vendor-provided and open source audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators.

Satisfies: SRG-OS-000256-GPOS-00097, SRG-OS-000257-GPOS-00098, SRG-OS-000258-GPOS-00099

Protecting audit information also includes identifying and protecting the tools used to view and manipulate log data. Therefore, protecting audit tools is necessary to prevent unauthorized operation on audit information.

Operating systems providing tools to interface with audit information will leverage user permissions and roles identifying the user accessing the tools and the corresponding rights the user enjoys in order to make access decisions regarding the access to audit tools.

Audit tools include, but are not limited to, vendor-provided and open source audit tools needed to successfully view and manipulate audit information system activity and records. Audit tools include custom queries and report generators.

Satisfies: SRG-OS-000256-GPOS-00097, SRG-OS-000257-GPOS-00098, SRG-OS-000258-GPOS-00099

If authorized individuals do not have the ability to modify auditing parameters in response to a changing threat environment, the organization may not be able to effectively respond, and important forensic information may be lost.

This requirement enables organizations to extend or limit auditing as necessary to meet organizational requirements. Auditing that is limited to conserve information system resources may be extended to address certain threat situations. In addition, auditing may be limited to a specific set of events to facilitate audit reduction, analysis, and reporting.

The report generation capability must support on-demand review and analysis in order to facilitate the organization's ability to generate incident reports, as needed, to better handle larger-scale or more complex security incidents. If the report generation capability does not support after-the-fact investigations, it is difficult to establish, correlate, and investigate the events leading up to an outage or attack, or identify those responses for one. This capability is also required to comply with applicable Federal laws and DoD policies.

Report generation must be capable of generating on-demand (i.e., customizable, ad hoc, and as-needed) reports. On-demand reporting allows personnel to report issues more rapidly to more effectively meet reporting requirements. Collecting log data and aggregating it to present the data in a single, consolidated report achieves this objective.

Satisfies: SRG-OS-000350-GPOS-00138, SRG-OS-000351-GPOS-00139, SRG-OS-000352-GPOS-00140

Rotate audit logs daily to preserve audit file system space and to conform to the DoD/DISA requirement. If it is not rotated daily and moved to another location, then there is more of a chance for the compromise of audit data by malicious users.

This telnet service is used to service remote user connections. This is historically the most commonly used remote access method for UNIX servers. The username and passwords are passed over the network in clear text and therefore insecurely. Unless required the telnetd daemon will be disabled. This function, if required, should be facilitated through SSH.

sudo command does not require reauthentication if NOPASSWD tag is specified in /etc/sudoers config file, or sudoers files in /etc/sudoers.d/ directory. With this tag in sudoers file, users are not required to reauthenticate for privilege escalation.

If a system has no default gateway defined, the system is at increased risk of man-in-the-middle, monitoring, and Denial of Service attacks.

If a system has no default gateway defined, the system is at increased risk of man-in-the-middle, monitoring, and Denial of Service attacks.

Only authorized personnel should be aware of errors and the details of the errors. Error messages are an indicator of an organization's operational state or can identify AIX or platform. Additionally, Personally Identifiable Information (PII) and operational information must not be revealed through error messages to unauthorized personnel or their designated representatives.

The structure and content of error messages must be carefully considered by the organization and development team. The extent to which the information system is able to identify and handle error conditions is guided by organizational policy and operational requirements.

Restricting permissions will protect the files from unauthorized modification.

Incorrect ownership of the cron or crontab directories could permit unauthorized users the ability to alter cron jobs and run automated jobs as privileged users. Failure to give ownership of cron or crontab directories to root or to bin provides the designated owner and unauthorized users with the potential to access sensitive information or change the system configuration which could weaken the system's security posture.

A synchronized system clock is critical for the enforcement of time-based policies and the correlation of logs and audit records with other systems. If an illicit time source is used for synchronization, the integrity of system logs and the security of the system could be compromised. If the configuration files controlling time synchronization are not owned by a system account, unauthorized modifications could result in the failure of time synchronization.

The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

System binaries are executed by privileged users as well as system services, and restrictive permissions are necessary to ensure that their execution of these programs cannot be co-opted.

If the Group Identifier (GID) of the home directory is not the same as the GID of the user, this would allow unauthorized access to files.

If the smbpasswd file has a mode more permissive than 0600, the smbpasswd file may be maliciously accessed or modified, potentially resulting in the compromise of Samba accounts.

The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

Without protection of the transmitted or received information, confidentiality and integrity may be compromised because unprotected communications can be intercepted and either read or altered.

Use of this requirement will be limited to situations where the data owner has a strict requirement for ensuring data integrity and confidentiality is maintained at every step of the data transfer and handling process. This requirement applies to both internal and external networks and all types of information system components from which information can be transmitted (e.g., servers, mobile devices, notebook computers, printers, copiers, scanners, and facsimile machines). Communication paths outside the physical protection of a controlled boundary are exposed to the possibility of interception and modification.

Protecting the confidentiality and integrity of organizational information can be accomplished by physical means (e.g., employing physical distribution systems) or by logical means (e.g., employing cryptographic techniques). If physical means of protection are employed, then logical means (cryptography) do not have to be employed, and vice versa.

Satisfies: SRG-OS-000423-GPOS-00187, SRG-OS-000424-GPOS-00188, SRG-OS-000425-GPOS-00189, SRG-OS-000426-GPOS-00190, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174

Remote access services, such as those providing remote access to network devices and information systems, which lack automated monitoring capabilities, increase risk and make remote user access management difficult at best.

Remote access is access to DoD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless.

Automated monitoring of remote access sessions allows organizations to detect cyberattacks and also ensure ongoing compliance with remote access policies by auditing connection activities of remote access capabilities, such as Remote Desktop Protocol (RDP), on a variety of information system components (e.g., servers, workstations, notebook computers, smartphones, and tablets).

The /etc/shells file lists approved default shells. It helps provide layered defense to the security approach by ensuring users cannot change their default shell to an unauthorized unsecure shell.

Automatic session termination addresses the termination of user-initiated logical sessions in contrast to the termination of network connections that are associated with communications sessions (i.e., network disconnect). A logical session (for local, network, and remote access) is initiated whenever a user (or process acting on behalf of a user) accesses an organizational information system. Such user sessions can be terminated (and thus terminate user access) without terminating network sessions.

Session termination terminates all processes associated with a user's logical session except those processes that are specifically created by the user (i.e., session owner) to continue after the session is terminated.

Conditions or trigger events requiring automatic session termination can include, for example, organization-defined periods of user inactivity, targeted responses to certain types of incidents, and time-of-day restrictions on information system use.

This capability is typically reserved for specific operating system functionality where the system owner, data owner, or organization requires additional assurance.
Satisfies: SRG-OS-000163-GPOS-00072

GSSAPI authentication is used to provide additional authentication mechanisms to applications. Allowing GSSAPI authentication through SSH exposes the system's GSSAPI to remote hosts, increasing the attack surface of the system. GSSAPI authentication must be disabled unless needed.

DoD information systems are required to use FIPS 140-2 approved cryptographic hash functions.

If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially with root privileges.

If reverse name checking is off, SSH may allow a remote attacker to circumvent security policies and attempt to or actually login from IP addresses that are not permitted to access resources.

X11 forwarding over SSH allows for the secure remote execution of X11-based applications. This feature can increase the attack surface of an SSH connection and should not be enabled unless needed.

When password authentication is allowed, PermitEmptyPasswords specifies whether the server allows login to accounts with empty password strings. If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

The SSH daemon should only listen on the approved listening IP addresses. Otherwise the SSH service could be subject to unauthorized access.

If a user cannot explicitly end an operating system session, the session may remain open and be exploited by an attacker; this is referred to as a zombie session. Users need to be aware of whether or not the session has been terminated.

Information resources to which users gain access via authentication include, for example, local workstations and remote services. Logoff messages can be displayed after authenticated sessions have been terminated. However, for some types of interactive sessions, including, for example, remote login, information systems typically send logoff messages as final messages prior to terminating sessions.

If a user cannot explicitly end an operating system session, the session may remain open and be exploited by an attacker; this is referred to as a zombie session. Users need to be aware of whether or not the session has been terminated.

Information resources to which users gain access via authentication include, for example, local workstations and remote services. Logoff messages can be displayed after authenticated sessions have been terminated. However, for some types of interactive sessions, including, for example, remote login, information systems typically send logoff messages as final messages prior to terminating sessions.

Unintentionally running a syslog server accepting remote messages puts the system at increased risk. Malicious syslog messages sent to the server could exploit vulnerabilities in the server software itself, could introduce misleading information in to the system's logs, or could fill the system's storage leading to a Denial of Service.

Without the capability to restrict which roles and individuals can select which events are audited, unauthorized personnel may be able to prevent the auditing of critical events. Misconfigured audits may degrade the system's performance by overwhelming the audit log. Misconfigured audits may also make it more difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Without the capability to restrict which roles and individuals can select which events are audited, unauthorized personnel may be able to prevent the auditing of critical events. Misconfigured audits may degrade the system's performance by overwhelming the audit log. Misconfigured audits may also make it more difficult to establish, correlate, and investigate the events relating to an incident or identify those responsible for one.

Automatic session termination addresses the termination of user-initiated logical sessions in contrast to the termination of network connections that are associated with communications sessions (i.e., network disconnect). A logical session (for local, network, and remote access) is initiated whenever a user (or process acting on behalf of a user) accesses an organizational information system. Such user sessions can be terminated (and thus terminate user access) without terminating network sessions.

Session termination terminates all processes associated with a user's logical session except those processes that are specifically created by the user (i.e., session owner) to continue after the session is terminated.

If a maintenance session or connection remains open after maintenance is completed, it may be hijacked by an attacker and used to compromise or damage the system.

Some maintenance and test tools are either standalone devices with their own operating systems or are applications bundled with an operating system.

Conditions or trigger events requiring automatic session termination can include, for example, organization-defined periods of user inactivity, targeted responses to certain types of incidents, and time-of-day restrictions on information system use.

This capability is typically reserved for specific operating system functionality where the system owner, data owner, or organization requires additional assurance.

Terminating network connections associated with communications sessions includes, for example, de-allocating associated TCP/IP address/port pairs at AIX level, and de-allocating networking assignments at the application level if multiple application sessions are using a single operating system-level network connection. This does not mean that AIX terminates all sessions or network access; it only ends the inactive session and releases the resources associated with that session.


Satisfies: SRG-OS-000279-GPOS-00109, SRG-OS-000163-GPOS-00072, SRG-OS-000126-GPOS-00066

The listed applications permit the transmission of passwords in plain text. Alternative applications such as SSH, which encrypt data, should be use instead.

Only authorized personnel should be aware of errors and the details of the errors. Error messages are an indicator of an organization's operational state or can identify AIX or platform. Additionally, Personally Identifiable Information (PII) and operational information must not be revealed through error messages to unauthorized personnel or their designated representatives.

The structure and content of error messages must be carefully considered by the organization and development team. The extent to which the information system is able to identify and handle error conditions is guided by organizational policy and operational requirements.

Unauthorized access could destroy the integrity of the library files.

The "/etc/group" file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

The NFS access option limits user access to the specified level. This assists in protecting exported file systems. If access is not restricted, unauthorized hosts may be able to access the system's NFS exports.

Excessive permissions on home directories allow unauthorized access to user files.

Without auditing the enforcement of access restrictions against changes to the application configuration, it will be difficult to identify attempted attacks and an audit trail will not be available for forensic investigation for after-the-fact actions.

Enforcement actions are the methods or mechanisms used to prevent unauthorized changes to configuration settings. Enforcement action methods may be as simple as denying access to a file based on the application of file permissions (access restriction). Audit items may consist of lists of actions blocked by access restrictions or changes identified after the fact.

Previous versions of software components that are not removed from the information system after updates have been installed may be exploited by adversaries. Some information technology products may remove older versions of software automatically from the information system.

Configuring a supplemental group for users permitted to switch to the root user prevents unauthorized users from accessing the root account, even with knowledge of the root credentials.

Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.

Command "mesg -n" allows only the root user the permission to send messages to your workstation to avoid having others clutter your display with incoming messages.

If Sendmail is not configured to log at level 9, system logs may not contain the information necessary for tracking unauthorized use of the sendmail service.

The rsh daemon permits username and passwords to be passed over the network in clear text.

The qdaemon program is the printing scheduling daemon that manages the submission of print jobs to the piobe service.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

The piobe daemon is the I/O back end for the printing process, handling the job scheduling and spooling.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

The rcnfs entry starts the NFS daemons during system boot.

NFS is a service with numerous historical vulnerabilities and should not be enabled unless there is no alternative. If NFS serving is required, then read-only exports are recommended and no filesystem or directory should be exported with root access. Unless otherwise required the NFS daemons (rcnfs) will be disabled.

The snmpd daemon is used by many 3rd party applications to monitor the health of the system. This allows remote monitoring of network and server configuration.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

The dhcprd daemon listens for broadcast packets, receives them, and forwards them to the appropriate server.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

This daemon provides gateway routing functions for protocols such as RIP and SNMP.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

This is the server for the DNS protocol and controls domain name resolution for its clients.

To prevent attacks this daemon should not be enabled unless there is no alternative.

This is the remote WHO service.

To prevent remote attacks this daemon should not be enabled unless there is no alternative.

The dpid2 daemon acts as a protocol converter, which enables DPI (SNMP v2) sub-agents, such as hostmibd, to talk to a SNMP v1 agent that follows SNMP MUX protocol.

To prevent attacks this daemon should not be enabled unless there is no alternative.

The aixmibd daemon is a dpi2 sub-agent which manages a number of MIB variables.

To prevent attacks this daemon should not be enabled unless there is no alternative.

This manages the Neighbor Discovery Protocol (NDP) for non-kernel activities, required in IPv6.

The ndpd-router manages NDP for non-kernel activities. Unless the server utilizes IPv6, this is not required and should be disabled to prevent attacks.

This is a calendar and appointment service for CDE.

The cmsd service is utilized by CDE to provide calendar functionality. If CDE is not required, this service should be disabled to prevent attacks.

This service facilitates file copying between networked servers.

The uucp (UNIX to UNIX Copy Program), service allows users to copy files between networked machines. Unless an application or process requires UUCP this should be disabled to prevent attacks.

This talk service is used to establish an interactive two-way communication link between two UNIX users. Unless required the talk service will be disabled to prevent attacks.

This service is used to test the integrity of TCP/IP packets arriving at the destination.

This chargen service is a character generator service and is used for testing the integrity of TCP/IP packets arriving at the destination. An attacker may spoof packets between machines running the chargen service and thus provide an opportunity for DoS attacks. Disable this service to prevent attacks unless testing the network.

The dtspc service deals with the CDE interface of the X11 daemon. It is started automatically by the inetd daemon in response to a CDE client requesting a process to be started on the daemon's host. This makes it vulnerable to buffer overflow attacks, which may allow an attacker to gain root privileges on a host. This service must be disabled unless it is absolutely required.

The rstatd service is used to provide kernel statistics and other monitorable parameters pertinent to the system such as: CPU usage, system uptime, network usage etc. An attacker may use this information in a DoS attack. This service should be disabled.

The sprayd service is used as a tool to generate UDP packets for testing and diagnosing network problems. The service must be disabled if NFS is not in use, as it can be used by attackers in a Distributed Denial of Service (DDoS) attack.

The kshell service offers a higher degree of security than traditional rsh services. However, it still does not use encrypted communications. The recommendation is to use SSH wherever possible instead of kshell.

If the kshell service is used, you should use the latest Kerberos version available and must make sure that all the latest patches are installed.

The tftp service allows remote systems to download or upload files to the tftp server without any authentication. It is therefore a service that should not run, unless needed. One of the main reasons for requiring this service to be activated is if the host is a NIM master. However, the service can be enabled and then disabled once a NIM operation has completed, rather than left running permanently.

The pop3 service provides a pop3 server. It supports the pop3 remote mail access protocol. It works with sendmail and bellmail. This service should be disabled if it is not required to prevent attacks.

The instsrv service is part of the Network Installation Tools, used for servicing servers running AIX 3.2. This service should be disabled to prevent attacks.

Internet Network News (INN) servers access Usenet newsfeeds and store newsgroup articles. INN servers use the Network News Transfer Protocol (NNTP) to transfer information from the Usenet to the server and from the server to authorized remote hosts.

If this function is necessary to support a valid mission requirement, its use must be authorized and approved in the system accreditation package.

The Reliable Datagram Sockets (RDS) protocol is a relatively new protocol developed by Oracle for communication between the nodes of a cluster. Binding this protocol to the network stack increases the attack surface of the host. Unprivileged local processes may be able to cause the system to dynamically load a protocol handler by opening a socket using the protocol.

AIX has RDS protocol installed as part of the 'bos.net.tcp.client' fileset. The RDS protocol in primarily used for communication on INFI-Band interfaces. The protocol is manually loaded with the bypassctrl command.

To prevent possible attacks this protocol must be disabled unless required.

A core dump includes a memory image taken at the time the operating system terminates an application. The memory image could contain sensitive data and is generally useful only for developers trying to debug problems.

DoS is a condition when a resource is not available for legitimate users. When this occurs, the organization either cannot accomplish its mission or must operate at degraded capacity.

Managing excess capacity ensures that sufficient capacity is available to counter flooding attacks. Employing increased capacity and service redundancy may reduce the susceptibility to some DoS attacks. Managing excess capacity may include, for example, establishing selected usage priorities, quotas, or partitioning.

Satisfies: SRG-OS-000142-GPOS-00071, SRG-OS-000480-GPOS-00227, SRG-OS-000433-GPOS-00192

Discretionary Access Control (DAC) is based on the notion that individual users are "owners" of objects and therefore have discretion over who should be authorized to access the object and in which mode (e.g., read or write). Ownership is usually acquired as a consequence of creating the object or via specified ownership assignment. DAC allows the owner to determine who will have access to objects they control. An example of DAC includes user-controlled file permissions.

When discretionary access control policies are implemented, subjects are not constrained with regard to what actions they can take with information for which they have already been granted access. Thus, subjects that have been granted access to information are not prevented from passing (i.e., the subjects have the discretion to pass) the information to other subjects or objects. A subject that is constrained in its operation by Mandatory Access Control policies is still able to operate under the less rigorous constraints of this requirement. Thus, while Mandatory Access Control imposes constraints preventing a subject from passing information to another subject operating at a different sensitivity level, this requirement permits the subject to pass the information to any subject at the same sensitivity level. The policy is bounded by the information system boundary. Once the information is passed outside the control of the information system, additional means may be required to ensure the constraints remain in effect. While the older, more traditional definitions of discretionary access control require identity-based access control, that limitation is not required for this use of discretionary access control.

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session.

Remote access is access to DoD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless.

Encryption provides a means to secure the remote connection to prevent unauthorized access to the data traversing the remote access connection (e.g., RDP), thereby providing a degree of confidentiality. The encryption strength of a mechanism is selected based on the security categorization of the information.

To mitigate the risk of unauthorized access to sensitive information by entities that have been issued certificates by DoD-approved PKIs, all DoD systems (e.g., web servers and web portals) must be properly configured to incorporate access control methods that do not rely solely on the possession of a certificate for access. Successful authentication must not automatically give an entity access to an asset or security boundary. Authorization procedures and controls must be implemented to ensure each authenticated entity also has a validated and current authorization. Authorization is the process of determining whether an entity, once authenticated, is permitted to access a specific asset. Information systems use access control policies and enforcement mechanisms to implement this requirement.

Access control policies include: identity-based policies, role-based policies, and attribute-based policies. Access enforcement mechanisms include: access control lists, access control matrices, and cryptography. These policies and mechanisms must be employed by the application to control access between users (or processes acting on behalf of users) and objects (e.g., devices, files, records, processes, programs, and domains) in the information system.

Security functions are the hardware, software, and/or firmware of the information system responsible for enforcing the system security policy and supporting the isolation of code and data on which the protection is based. Operating systems implement code separation (i.e., separation of security functions from nonsecurity functions) in a number of ways, including through the provision of security kernels via processor rings or processor modes. For non-kernel code, security function isolation is often achieved through file system protections that serve to protect the code on disk and address space protections that protect executing code.

Discretionary Access Control (DAC) is based on the notion that individual users are "owners" of objects and therefore have discretion over who should be authorized to access the object and in which mode (e.g., read or write). Ownership is usually acquired as a consequence of creating the object or via specified ownership assignment. DAC allows the owner to determine who will have access to objects they control. An example of DAC includes user-controlled file permissions.

Operating system functionality will vary, and while users are not permitted to install unapproved software, there may be instances where the organization allows the user to install approved software packages, such as from an approved software repository.

AIX or software configuration management utility must enforce control of software installation by users based upon what types of software installations are permitted (e.g., updates and security patches to existing software) and what types of installations are prohibited (e.g., software whose pedigree with regard to being potentially malicious is unknown or suspect) by the organization.

Satisfies: SRG-OS-000080-GPOS-00048, SRG-OS-000134-GPOS-00068, SRG-OS-000312-GPOS-00123, SRG-OS-000362-GPOS-00149

The rwalld service allows remote users to broadcast system wide messages. The service runs as root and should be disabled unless absolutely necessary to prevent attacks.

The shells file (or equivalent) lists approved default shells. It helps provide layered defense to the security approach by ensuring users cannot change their default shell to an unauthorized unsecure shell.

The ability to boot from removable media is the same as being able to boot into single user or maintenance mode without a password. This ability could allow a malicious user to boot the system and perform changes possibly compromising or damaging the system. It could also allow the system to be used for malicious purposes by a malicious anonymous user.

The version of the SMTP service can be used by attackers to plan an attack based on vulnerabilities present in the specific version.

Debug mode is a feature present in older versions of Sendmail which, if not disabled, may allow an attacker to gain access to a system through the Sendmail service.

Failure to restrict system access to authenticated users negatively impacts operating system security.

The use of hard-to-guess NIS domain names provides additional protection from unauthorized access to the NIS directory information.

Failure to restrict system access to authenticated users negatively impacts operating system security.

The library preload list environment variable contains a list of libraries for the dynamic linker to load before loading the libraries required by the binary. If this list contains paths to libraries relative to the current working directory, unintended libraries may be preloaded.

The library search path environment variable(s) contain a list of directories for the dynamic linker to search to find libraries. If this path includes the current working directory or other relative paths, libraries in these directories may be loaded instead of system libraries. This variable is formatted as a colon-separated list of directories. If there is an empty entry, such as a leading or trailing colon, or two consecutive colons, this is interpreted as the current working directory.

Verification using the system package management tool can be used to determine that system software has not been tampered with. This requirement is not applicable to systems not using package management tools.

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this software is used when not required, system network information may be unnecessarily transmitted across the network.

Responding to broadcast ICMP echo requests facilitates network mapping and provides a vector for amplification attacks.

Trust files are convenient, but when used in conjunction with the remote login services, they can allow unauthenticated access to a system.

Changing the root home directory to something other than / and assigning it a 0700 protection makes it more difficult for intruders to manipulate the system by reading the files that root places in its default directory. It also gives root the same discretionary access control for root's home directory as for the other plain user home directories.

To assure accountability and prevent unauthenticated access, privileged and non-privileged users must utilize multifactor authentication to prevent potential misuse and compromise of the system.
Multifactor authentication uses two or more factors to achieve authentication.

Factors include:
1. Something you know (e.g., password/PIN);
2. Something you have (e.g., cryptographic identification device, token); and
3. Something you are (e.g., biometric).

The DoD CAC with DoD-approved PKI is an example of multifactor authentication.


Satisfies: SRG-OS-000105-GPOS-00052, SRG-OS-000106-GPOS-00053, SRG-OS-000107-GPOS-00054, SRG-OS-000108-GPOS-00055, SRG-OS-000375-GPOS-00160

To assure accountability and prevent unauthenticated access, privileged and non-privileged users must utilize multifactor authentication to prevent potential misuse and compromise of the system.
Multifactor authentication uses two or more factors to achieve authentication.

Factors include:
1. Something you know (e.g., password/PIN);
2. Something you have (e.g., cryptographic identification device, token); and
3. Something you are (e.g., biometric).

The DoD CAC with DoD-approved PKI is an example of multifactor authentication.

To assure accountability and prevent unauthenticated access, privileged and non-privileged users must utilize multifactor authentication to prevent potential misuse and compromise of the system.
Multifactor authentication uses two or more factors to achieve authentication.

Factors include:
1. Something you know (e.g., password/PIN);
2. Something you have (e.g., cryptographic identification device, token); and
3. Something you are (e.g., biometric).

The DoD CAC with DoD-approved PKI is an example of multifactor authentication.

Failure to restrict network connectivity only to authorized systems permits inbound connections from malicious systems. It also permits outbound connections that may facilitate exfiltration of DoD data.

Unauthorized ownership of the /etc/hosts file can lead to the ability for a malicious actor to redirect traffic to servers of their choice. It is also possible to use the /etc/hosts file to block detection by security software by blocking the traffic to all the download or update servers of well-known security vendors.

Unauthorized permissions of the /etc/hosts file can lead to the ability for a malicious actor to redirect traffic to servers of their choice. It is also possible to use the /etc/hosts file to block detection by security software by blocking the traffic to all the download or update servers of well-known security vendors.

Unauthorized ownership of the /etc/syslog.conf file can lead to the ability for a malicious actor to alter or disrupt system logging activities. This can aid the malicious actor in avoiding detection and further their ability to conduct malicious activities on the system.

Unauthorized permissions of the /etc/syslog.conf file can lead to the ability for a malicious actor to alter or disrupt system logging activities. This can aid the malicious actor in avoiding detection and further their ability to conduct malicious activities on the system.

Failure to set proper permissions of sensitive files or utilities may provide unauthorized users with the potential to access sensitive information or change the system configuration which could weaken the system's security posture.

Unauthorized group ownership of the /var/spool/cron/atjobs directory could permit unauthorized users the ability to alter atjobs and run automated jobs as privileged users. Failure to set proper permissions of the /var/spool/cron/atjobs directory provides unauthorized users with the potential to access sensitive information or change the system configuration which could weaken the system's security posture.

Incorrect group ownership of the cron or crontab directories could permit unauthorized users the ability to alter cron jobs and run automated jobs as privileged users. Failure to give ownership of cron or crontab directories to root or to bin provides the designated owner and unauthorized users with the potential to access sensitive information or change the system configuration which could weaken the system's security posture.