SV-219287r991577: The Ubuntu operating system must generate audit records upon successful/unsuccessful use of unlink, unlinkat, rename, renameat, and rmdir system calls. | Canonical Ubuntu 18.04 LTS STIG SCAP Benchmark

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Assessment Title

Rule Text

The Ubuntu operating system must generate audit records upon successful/unsuccessful use of unlink, unlinkat, rename, renameat, and rmdir system calls.

Description

Discussion Text

Without generating audit records that are specific to the security and mission needs of the organization, 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 system call rules are loaded into a matching engine that intercepts each syscall made by all programs on the system. Therefore, it is very important to use syscall rules only when absolutely necessary since these affect performance. The more rules, the bigger the performance hit. The performance is helped, however, by combining syscalls into one rule whenever possible.

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-000172V-100797SV-109901

References

DPMS Target Canonical Ubuntu 18.04 LTS DISA DPMS Target Canonical Ubuntu 18.04 LTS 4055

Checks

DISA STIG (Manual Reference)

Verify the Ubuntu operating system generates audit records upon successful/unsuccessful use of "unlink", "unlinkat", "rename", "renameat", and "rmdir" system calls.

Check the currently configured audit rules with the following command:

# sudo auditctl -l | grep 'unlink\|rename\|rmdir'

-a always,exit -F arch=b64 -S unlink,unlinkat,rename,renameat,rmdir -F auid>=1000 -F auid!=-1 -k delete
-a always,exit -F arch=b32 -S unlink,unlinkat,rename,renameat,rmdir -F auid>=1000 -F auid!=-1 -k delete

If the command does not return audit rules for the "unlink", "unlinkat", "rename", "renameat", and "rmdir" syscalls or the lines are commented out, this is a finding.

Notes:
For 32-bit architectures, only the 32-bit specific output lines from the commands are required.
The "-k" allows for specifying an arbitrary identifier and the string after it does not need to match the example output above.

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

#!/bin/bash
# Reconstructed from oval:mil.disa.stig.ubuntu1804:def:229
# The Ubuntu operating system must generate audit records upon successful/unsuccessful use of unlink, unlinkat, rename, renameat, and rmdir system calls.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# auditd package is installed
# dpkginfo_object (dpkginfo_test)
test_1() {
  grep -A1 '^Package: auditd$' /var/lib/dpkg/status &>/dev/null
}
# check for running auditd
# process58_object (process58_test)
test_2() {
  ps -eo args | grep -P '^\/sbin\/auditd\b' &>/dev/null
}
# Audit 32-bit invocations of unlink syscall
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b32\s+(?:.*(-S[\s]+unlink[\s]+|([\s]+|[,])unlink([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of unlink syscall
# textfilecontent54_object (textfilecontent54_test)
test_4() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S[\s]+unlink[\s]+|([\s]+|[,])unlink([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 32-bit invocations of unlinkat syscall
# textfilecontent54_object (textfilecontent54_test)
test_5() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b32\s+(?:.*(-S[\s]+unlinkat[\s]+|([\s]+|[,])unlinkat([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of unlinkat syscall
# textfilecontent54_object (textfilecontent54_test)
test_6() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S[\s]+unlinkat[\s]+|([\s]+|[,])unlinkat([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 32-bit invocations of rename syscall
# textfilecontent54_object (textfilecontent54_test)
test_7() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b32\s+(?:.*(-S[\s]+rename[\s]+|([\s]+|[,])rename([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of rename syscall
# textfilecontent54_object (textfilecontent54_test)
test_8() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S[\s]+rename[\s]+|([\s]+|[,])rename([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 32-bit invocations of renameat syscall
# textfilecontent54_object (textfilecontent54_test)
test_9() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b32\s+(?:.*(-S[\s]+renameat[\s]+|([\s]+|[,])renameat([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of renameat syscall
# textfilecontent54_object (textfilecontent54_test)
test_10() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S[\s]+renameat[\s]+|([\s]+|[,])renameat([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 32-bit invocations of rmdir syscall
# textfilecontent54_object (textfilecontent54_test)
test_11() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b32\s+(?:.*(-S[\s]+rmdir[\s]+|([\s]+|[,])rmdir([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of rmdir syscall
# textfilecontent54_object (textfilecontent54_test)
test_12() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S[\s]+rmdir[\s]+|([\s]+|[,])rmdir([\s]+|[,])).*)-F\s+auid>=1000\s+-F\s+auid!=(unset|-1|4294967295).*(-k[\s]+|-F[\s]+key=)[-\w]+[\s]*$' '/etc/audit/audit.rules' &>/dev/null
}

if ( test_1 && test_2 && test_3 && test_4 && test_5 && test_6 && test_7 && test_8 && test_9 && test_10 && test_11 && test_12 ); then
  echo "PASS"
else
  echo "FAIL"
fi

Assessment Script Powered by AISandbox-executed

A standalone Shell script to assess this control automatically. Review before running it in your environment.

Syntax-checked and actually executed in an isolated sandbox (not the real system this checks) — confirmed to run without errors.

#!/bin/sh
# OVAL Definition: oval:mil.disa.stig.ubuntu1804:def:229
if [ ! -x "$(command -v dpkg)" ]; then echo "FAIL"; exit 1; fi
if [ ! -x "$(command -v auditd)" ]; then echo "FAIL"; exit 1; fi
if ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+-S\\s+unlink\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+-S\\s+unlinkat\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+-S\\s+rename\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+-S\\s+renameat\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+-S\\s+rmdir\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ]; then echo "FAIL"; exit 1; fi
if ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+-S\\s+unlink\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+-S\\s+unlinkat\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+-S\\s+rename\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+-S\\s+renameat\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ] && ! grep -q '^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+-S\\s+rmdir\\s+-F\\s+auid>=1000\\s+-F\\s+auid != 4294967295\\s+-k\\s+delete' /etc/audit/rules.d/stig.rules ]; then echo "FAIL"; exit 1; fi
echo "PASS"; exit 0

Remediation

Configure the audit system to generate audit events upon successful/unsuccessful use of "unlink", "unlinkat", "rename", "renameat", and "rmdir" system calls.

Add or update the following rules in the "/etc/audit/rules.d/stig.rules" file:

-a always,exit -F arch=b64 -S unlink,unlinkat,rename,renameat,rmdir -Fauid>=1000 -F auid!=4294967295 -k delete
-a always,exit -F arch=b32 -S unlink,unlinkat,rename,renameat,rmdir -F auid>=1000 -F auid!=4294967295 -k delete

Notes: For 32-bit architectures, only the 32-bit specific entries are required. 
The "root" account must be used to view/edit any files in the /etc/audit/rules.d/ directory.

To reload the rules file, issue the following command:

# sudo augenrules --load