SV-281309r1184631: RHEL 10 must enable kernel parameters to enforce discretionary access control (DAC) on hardlinks. | Red Hat Enterprise Linux 10 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 10 must enable kernel parameters to enforce discretionary access control (DAC) 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 systems accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). Satisfies: SRG-OS-000312-GPOS-00122, 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 Red Hat Enterprise Linux 10 DISA DPMS Target Red Hat Enterprise Linux 10 5733

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.rhel10os:def:281309
# RHEL 10 must enable kernel parameters to enforce discretionary access control (DAC) 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.rhel10os:def:281309

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

if [ -f /etc/sysctl.d/99-fs_protected_hardlinks.conf ]; then
    grep -q '^fs\.protected_hardlinks = 1$' /etc/sysctl.d/99-fs_protected_hardlinks.conf
    if [ $? -eq 0 ]; then
        echo "PASS"
        exit 0
    else
        echo "FAIL"
        exit 1
    fi
else
    echo "PASS"
    exit 0
fi

Remediation

Configure RHEL 10 to enable DAC on hardlinks.

Create a drop-in if it does not already exist:

$ sudo vi /etc/sysctl.d/99-fs_protected_hardlinks.conf

Add the following to the file:

fs.protected_hardlinks = 1

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

$ sudo sysctl --system