SV-258003r1045065: RHEL 9 SSH daemon must not allow GSSAPI authentication. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 9 SSH daemon must not allow GSSAPI authentication.

Description

Discussion Text

Generic Security Service Application Program Interface (GSSAPI) authentication is used to provide additional authentication mechanisms to applications. Allowing GSSAPI authentication through SSH exposes the system's GSSAPI to remote hosts, increasing the attack surface of the system. Satisfies: SRG-OS-000364-GPOS-00151, SRG-OS-000480-GPOS-00227

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

IA Controls

NIST SP 800-53

Not mappedCCI-001813

References

DPMS Target Red Hat Enterprise Linux 9 DISA DPMS Target Red Hat Enterprise Linux 9 5551

Checks

DISA STIG (Manual Reference)

Verify the SSH daemon does not allow GSSAPI authentication with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*gssapiauthentication'

GSSAPIAuthentication no

If the value is returned as "yes", the returned line is commented out, no output is returned, and the use of GSSAPI authentication has not been documented with the information system security officer (ISSO), this is a finding.

If the required value is not set, this is a finding.

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.rhel9os:def:258003
# RHEL 9 SSH daemon must not allow GSSAPI authentication.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# sshd_config includes sshd_config.d
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (sed -En 's/^\s*include\s+(.*)\s*$/\1/p' '/etc/ssh/sshd_config') | grep -qxF '/etc/ssh/sshd_config.d/*.conf'
}
# /etc/ssh/sshd_config.d: GSSAPIAuthentication is set to no
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (grep -rhP --include='*.conf' '^\s*(?i)GSSAPIAuthentication(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$' '/etc/ssh/sshd_config.d' | sed -En 's/^\s*(?i)GSSAPIAuthentication(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$/\1/p') | grep -Pq '^(no|"no")$'
}
# /etc/ssh/sshd_config: GSSAPIAuthentication is set to no
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  (sed -En 's/^\s*(?i)GSSAPIAuthentication(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(no|"no")$'
}

if ( ( test_1 && test_2 ) || test_3 ); 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.rhel9os:def:258003

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

if [ $(grep -c "^GSSAPIAuthentication[[:space:]]*no" /etc/ssh/sshd_config.d/*.conf) -ge 1 ]; then
    echo "PASS"
    exit 0
fi

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

if [ $(grep -c "^GSSAPIAuthentication[[:space:]]*no" /etc/ssh/sshd_config) -ge 1 ]; then
    echo "PASS"
    exit 0
fi

echo "FAIL"
exit 1

Remediation

Configure the SSH daemon to not allow GSSAPI authentication.

Add or uncomment the following line to "/etc/ssh/sshd_config" or to a file in "/etc/ssh/sshd_config.d" and set the value to "no":

GSSAPIAuthentication no

The SSH service must be restarted for changes to take effect:

$ sudo systemctl restart sshd.service