SV-281255r1184755: RHEL 10 must be configured so that the Secure Shell (SSH) daemon does not allow Kerberos authentication. | Red Hat Enterprise Linux 10 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 10 must be configured so that the Secure Shell (SSH) daemon does not allow Kerberos authentication.

Description

Discussion Text

Kerberos authentication for SSH is often implemented using Generic Security Service Application Program Interface (GSSAPI). If Kerberos is enabled through SSH, the SSH daemon provides a means of access to the system's Kerberos implementation. Vulnerabilities in the system's Kerberos implementations may be subject to exploitation. 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-001813

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:281255
# RHEL 10 must be configured so that the Secure Shell (SSH) daemon does not allow Kerberos authentication.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# /etc/ssh/sshd_config:KerberosAuthentication == no
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (sed -En 's/^\s*(?i)KerberosAuthentication(?-i)\s+("?\w+"?)\s*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(no|"no")$'
}
# /etc/ssh/sshd_config does not include sshd_config.d
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\s*include\s+(.*)\s*$/\1/p' '/etc/ssh/sshd_config') | grep -qxF '/etc/ssh/sshd_config.d/*.conf'
}
# /etc/ssh/sshd_config includes sshd_config.d
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  (sed -En 's/^\s*include\s+(.*)\s*$/\1/p' '/etc/ssh/sshd_config') | grep -qxF '/etc/ssh/sshd_config.d/*.conf'
}
# /etc/ssh/sshd_config + sshd_config.d:KerberosAuthentication == no
# textfilecontent54_object (textfilecontent54_test)
test_4() {
  ( (sed -En 's/^\s*(?i)KerberosAuthentication(?-i)\s+("?\w+"?)\s*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(no|"no")$' ) || ( (grep -rhP --include='*.conf' '^\s*(?i)KerberosAuthentication(?-i)\s+("?\w+"?)\s*(?:|(?:#.*))?$' '/etc/ssh/sshd_config.d' | sed -En 's/^\s*(?i)KerberosAuthentication(?-i)\s+("?\w+"?)\s*(?:|(?:#.*))?$/\1/p') | grep -Pq '^(no|"no")$' )
}

if ( ( test_1 && test_2 ) || ( test_3 && test_4 ) ); 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:281255

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

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

grep -q "^KerberosAuthentication.*no$" /etc/ssh/sshd_config || \
grep -q "^KerberosAuthentication.*no$" /etc/ssh/sshd_config.d/*.conf

if [ $? -eq 0 ]; then
  echo "PASS"
  exit 0
fi

echo "FAIL"
exit 1

Remediation

Configure RHEL 10 SSH daemons to not allow Kerberos authentication.

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

KerberosAuthentication no

Restart the SSH service with the following command for the changes to take effect:

$ sudo systemctl restart sshd.service