SV-253000r958412: Successful/unsuccessful uses of the "unlink" command in TOSS must generate an audit record. | Tri-Lab Operating System Stack (TOSS) 4 STIG SCAP Benchmark

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Assessment Title

Rule Text

Successful/unsuccessful uses of the "unlink" command in TOSS must generate an audit record.

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 "unlink" command deletes a name from the filesystem. If that name was the last link to a file and no processes have the file open, the file is deleted and the space it was using is made available for reuse. When a user logs on, the AUID is set to the UID of the account that is being authenticated. Daemons are not user sessions and have the loginuid set to "-1." The AUID representation is an unsigned 32-bit integer, which equals "4294967295." The audit system interprets "-1", "4294967295", and "unset" in the same way. Satisfies: SRG-OS-000037-GPOS-00015, SRG-OS-000042-GPOS-00020, SRG-OS-000062-GPOS-00031, SRG-OS-000392-GPOS-00172, SRG-OS-000462-GPOS-00206, SRG-OS-000468-GPOS-00212, SRG-OS-000471-GPOS-00215

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

IA Controls

NIST SP 800-53

Not mappedCCI-000130Not mappedCCI-000135Not mappedCCI-000169Not mappedCCI-000172Not mappedCCI-002884

References

DPMS Target TOSS 4 DISA DPMS Target TOSS 4 5469

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.toss4os:def:253000
# Successful/unsuccessful uses of the "unlink" command in TOSS must generate an audit record.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# Audit 32-bit invocations of unlink
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  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!=(4294967295|-1|unset)(\s+(-k\s+|-F\s+key=)[-\w]+)*\s*$' '/etc/audit/audit.rules' &>/dev/null
}
# Audit 64-bit invocations of unlink
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  grep -Pq '^\s*-a\s+(always,exit|exit,always)\s+-F\s+arch=b64\s+(?:.*(-S\s+unlink\s+|(\s+|,)unlink(\s+|,))).*-F\s+auid>=1000\s+-F\s+auid!=(4294967295|-1|unset)(\s+(-k\s+|-F\s+key=)[-\w]+)*\s*$' '/etc/audit/audit.rules' &>/dev/null
}

if ( test_1 && test_2 ); 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.toss4os:def:253000


if [ ! -f "/etc/audit/rules.d/audit.rules" ]; then
  echo "FAIL"
  exit 1
fi

if [ $(grep -c "^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b32\\s+(?:.*(-S\\s+unlink\\s+|(\\s+|,)unlink(\\s+|,))).*-F\\s+auid>=1000\\s+-F\\s+auid != (4294967295|-1|unset)(\\s+(-k\\s+|-F\\s+key=)[-\\w]+)*\\s*$" /etc/audit/rules.d/audit.rules) -ge 1 ] && \
   [ $(grep -c "^\\s*-a\\s+(always,exit|exit,always)\\s+-F\\s+arch=b64\\s+(?:.*(-S\\s+unlink\\s+|(\\s+|,)unlink(\\s+|,))).*-F\\s+auid>=1000\\s+-F\\s+auid != (4294967295|-1|unset)(\\s+(-k\\s+|-F\\s+key=)[-\\w]+)*\\s*$" /etc/audit/rules.d/audit.rules) -ge 1 ]; then
  echo "PASS"
  exit 0
else
  echo "FAIL"
  exit 1
fi

Remediation

Configure the audit system to generate an audit event for any successful/unsuccessful use of the "unlink" syscall by adding or updating the following rules in the "/etc/audit/rules.d/audit.rules" file:

-a always,exit -F arch=b32 -S unlink -F auid>=1000 -F auid!=unset -k delete
-a always,exit -F arch=b64 -S unlink -F auid>=1000 -F auid!=unset -k delete

The audit daemon must be restarted for the changes to take effect.