SV-40723r1: The SSH daemon must not allow compression or must only allow compression after successful authentication. | AIX 6.1 SECURITY TECHNICAL IMPLEMENTATION GUIDE

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Assessment Title

Rule Text

The SSH daemon must not allow compression or must only allow compression after successful authentication.

Description

Discussion Text

If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially with root privileges.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000366

Additional Details

Responsibility

System Administrator

IA Controls

ECSC-1

References

DPMS Target AIX 6.1 DISA DPMS Target AIX 6.1 2176

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.fso.aix11:def:327
# The SSH daemon must not allow compression or must only allow compression after successful authentication.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# Compression Setting OK
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (sed -En 's/^[ 	]*[Cc][Oo][Mm][Pp][Rr][Ee][Ss][Ss][Ii][Oo][Nn][ 	]+(yes|no|delayed)[ 	]*$/\1/p' '/etc/ssh/sshd_config') | grep -Pq 'no|delayed'
}

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
# Shell script implementing OVAL definition oval:mil.disa.fso.aix11:def:327

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

grep -E "^[ \t]*[Cc][Oo][Mm][Pp][Rr][Ee][Ss][Ii][Oo][Nn][ \t]+(yes|no|delayed)[ \t]*$" "$FILE" | \
awk '{if ($NF == "no" || $NF == "delayed") print "PASS"; else print "FAIL"}'
if [ $? -ne 0 ]; then
  echo "FAIL"
  exit 1
fi
echo "PASS"
exit 0

Remediation

Edit the /etc/ssh/sshd_config file and remove the Compression setting or set the Compression setting to "delayed" or "no".