SV-274169r1120495: Amazon Linux 2023 must enable discretionary access control on hardlinks. | Amazon Linux 2023 STIG SCAP Benchmark

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Assessment Title

Rule Text

Amazon Linux 2023 must enable discretionary access control on hardlinks.

Description

Discussion Text

By enabling the fs.protected_hardlinks kernel parameter, users can no longer create soft or hard links to files they do not own. Disallowing such hardlinks mitigates vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). Satisfies: SRG-OS-000312-GPOS-00123, SRG-OS-000324-GPOS-00125

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

IA Controls

NIST SP 800-53

Not mappedCCI-002165Not mappedCCI-002235

References

DPMS Target Amazon Linux 2023 DISA DPMS Target Amazon Linux 2023 5700

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.amzlx23os:def:274169
# Amazon Linux 2023 must enable discretionary access control on hardlinks.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# fs.protected_hardlinks setting in kernel is 1
# sysctl_object (sysctl_test)
test_1() {
  [ "$(cat /proc/sys/fs/protected_hardlinks)" -eq 1 ]
}

if test_1; 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:mil.disa.stig.amzlx23os:def:274169

if ! command -v sysctl >/dev/null 2>&1; then
  echo "FAIL"
  exit 1
fi

if [ ! -f "/etc/sysctl.d/00-default.conf" ]; then
  echo "PASS"
  exit 0
fi

if grep -q "^fs.protected_hardlinks = 1$" /etc/sysctl.d/00-default.conf; then
  echo "PASS"
  exit 0
fi

echo "FAIL"
exit 1

Remediation

Configure Amazon Linux 2023 to enable DAC on hardlinks with the following:

Add or edit the following line in a system configuration file in the "/etc/sysctl.d/" directory:

fs.protected_hardlinks = 1

Load settings from all system configuration files with the following command:

$ sudo sysctl --system