SV-281267r1184767: RHEL 10 must not allow users to override Secure Shell (SSH) environment variables. | Red Hat Enterprise Linux 10 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 10 must not allow users to override Secure Shell (SSH) environment variables.

Description

Discussion Text

SSH environment options potentially allow users to bypass access restriction in some configurations. OpenSSH uses the first occurrence of a keyword it sees, and drop-in files are read in lexicographical order at the start of the configuration. Red Hat recommends using drop-in files rather than changing base configuration files.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000381

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:281267
# RHEL 10 must not allow users to override Secure Shell (SSH) environment variables.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# Check to see if PermitUserEnvironment is set to no in /etc/ssh/sshd_config and /etc/ssh/sshd_config.d/*.conf
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  ( (sed -En 's/^(?i)\s*PermitUserEnvironment\s+(\w+)$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(no|"no")$' ) || ( (grep -rhP --include='*.conf' '^(?i)\s*PermitUserEnvironment\s+(\w+)$' '/etc/ssh/sshd_config.d' | sed -En 's/^(?i)\s*PermitUserEnvironment\s+(\w+)$/\1/p') | grep -Pq '^(no|"no")$' )
}

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 definition: oval:mil.disa.stig.rhel10os:def:281267

if [ ! -f "/etc/ssh/sshd_config" ] || [ ! -f "/etc/ssh/sshd_config.d" ]; then
  echo "PASS"
  exit 0
fi

grep -qE "^(?:\s*PermitUserEnvironment\s+)?(no)$" /etc/ssh/sshd_config || echo "FAIL" && exit 1
grep -qE "^(?:\s*PermitUserEnvironment\s+)?(no)$" /etc/ssh/sshd_config.d/*.conf || echo "FAIL" && exit 1

echo "PASS"
exit 0

Remediation

Configure RHEL 10 to disable unattended or automatic login via SSH.

In "/etc/ssh/sshd_config.d", create a drop file that will lexicographically precede 50-redhat.conf and add the following line:

PermitUserEnvironment no

Restart the SSH daemon with the following command for the setting to take effect:

$ sudo systemctl restart sshd.service