Ubuntu24 Stig

ubuntu24-stig

DISA STIG V1R1 hardening for Ubuntu 24.04 LTS on AWS EC2. Covers OpenSCAP scanning, idempotent shell remediation for MAC-2_Sensitive, and a catalogue of the most common failures with their exact fixes.

When to use

• Running an OpenSCAP SCAP scan with U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.xml
• Applying MAC-2_Sensitive or MAC-2_Public remediation via shell script
• Fixing individual failing STIG rules (auditd, SSH, PAM, AIDE, sysctl)
• Reviewing a scan result and explaining what each fail means
• Preparing an AWS EC2 instance for a STIG compliance audit

Do NOT use for:

• Ubuntu 22.04 (different STIG benchmark — use U_CAN_Ubuntu_22-04_LTS V1R2)
• Non-Ubuntu distros (RHEL, Amazon Linux have separate benchmarks)
• Graphical workstation hardening (most GUI rules are notapplicable on headless EC2)

Step 1 — Download the STIG benchmark

Official source: https://public.cyber.mil/stigs/downloads/
Search: Ubuntu 24.04
File: U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.zip
Extract: U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.xml

Place at: /opt/stig/U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.xml

Step 2 — Install OpenSCAP (Ubuntu 24.04 package names)

apt-get update
apt-get install -y openscap-scanner openscap-common bzip2

Ubuntu 24.04 package change: libopenscap8 was replaced by libopenscap25t64. Use openscap-scanner — it pulls the correct library automatically. Do NOT install libopenscap8.

Step 3 — Correct SCAP benchmark IDs

The IDs in the XML for V1R1 are:

Common error: Using xccdf_mil.disa.stig_benchmark_CAN_Ubuntu_24-04_STIG (missing _LTS) causes
Failed to locate a datastream — always include _LTS_ in the benchmark ID.

Verify IDs from the file:

grep -o 'id="[^"]*benchmark[^"]*"' /opt/stig/U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.xml | head -5

Step 4 — Run a scan

BENCHMARK=/opt/stig/U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark.xml
PROFILE=xccdf_mil.disa.stig_profile_MAC-2_Sensitive
OUTDIR=/var/log/stig

mkdir -p "$OUTDIR"

oscap xccdf eval \
  --datastream-id scap_mil.disa.stig_datastream_U_CAN_Ubuntu_24-04_LTS_V1R1_STIG_SCAP_1-3_Benchmark \
  --xccdf-id xccdf_mil.disa.stig_benchmark_CAN_Ubuntu_24-04_LTS_STIG \
  --profile "$PROFILE" \
  --results "$OUTDIR/results.xml" \
  --report  "$OUTDIR/report.html" \
  "$BENCHMARK" || true   # exit code 2 = findings present, not a script error

echo "Report: $OUTDIR/report.html"

Step 5 — Remediation script

See remediate-mac2-sensitive.sh in this skill directory.
Run as root on a snapshot/AMI first — this changes system configuration.

chmod +x remediate-mac2-sensitive.sh
sudo ./remediate-mac2-sensitive.sh 2>&1 | tee /var/log/stig-remediation.log

AWS EC2 skip list

The following rules are notapplicable or impractical on headless EC2 and are skipped by the script:

Top failure categories and fixes

auditd not installed (SV-270656, SV-270657)

apt-get install -y auditd audispd-plugins
systemctl enable --now auditd

AIDE integrity monitoring (SV-270649, SV-270652)

apt-get install -y aide aide-common
aideinit
mv /var/lib/aide/aide.db.new /var/lib/aide/aide.db
# Cron check:
echo "0 5 * * * root /usr/bin/aide --check | mail -s 'AIDE report' root" > /etc/cron.d/aide

SSH FIPS 140-3 ciphers (SV-270667 to SV-270671)

cat >> /etc/ssh/sshd_config.d/99-stig-fips.conf << 'EOF'
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
MACs hmac-sha2-256,hmac-sha2-512,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com
KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256
X11Forwarding no
X11UseLocalhost yes
PrintLastLog yes
PermitEmptyPasswords no
PermitUserEnvironment no
ClientAliveInterval 600
ClientAliveCountMax 0
EOF
systemctl restart sshd

SSH client FIPS (SV-270670, SV-270671)

cat >> /etc/ssh/ssh_config.d/99-stig-fips.conf << 'EOF'
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
MACs hmac-sha2-256,hmac-sha2-512,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com
EOF

PAM pwquality (SV-270704, SV-270705, SV-270726–270733)

apt-get install -y libpam-pwquality
cat > /etc/security/pwquality.conf << 'EOF'
minlen = 15
ucredit = -1
lcredit = -1
dcredit = -1
ocredit = -1
difok = 8
dictcheck = 1
EOF

PAM lockout after 3 attempts (SV-270690)

cat > /etc/security/faillock.conf << 'EOF'
deny = 3
unlock_time = 0
fail_interval = 900
EOF

Password aging (SV-270730, SV-270731)

sed -i 's/^PASS_MAX_DAYS.*/PASS_MAX_DAYS   60/' /etc/login.defs
sed -i 's/^PASS_MIN_DAYS.*/PASS_MIN_DAYS   1/'  /etc/login.defs

Concurrent sessions limit (SV-270677)

echo "* hard maxlogins 10" >> /etc/security/limits.d/99-stig.conf

Session inactivity timeout (SV-270680)

cat > /etc/profile.d/99-stig-tmout.sh << 'EOF'
TMOUT=600
readonly TMOUT
export TMOUT
EOF

Disable Ctrl-Alt-Delete (SV-270712)

systemctl mask ctrl-alt-del.target
systemctl daemon-reload

Disable USB mass storage (SV-270718)

echo "install usb-storage /bin/true" > /etc/modprobe.d/disable-usb-storage.conf

Kernel sysctl hardening (SV-270749, SV-270753)

cat >> /etc/sysctl.d/99-stig.conf << 'EOF'
kernel.dmesg_restrict = 1
net.ipv4.tcp_syncookies = 1
EOF
sysctl --system

APT autoremove (SV-270773)

apt-get -y autoremove
echo 'APT::Get::AutomaticRemove "true";' > /etc/apt/apt.conf.d/99autoremove

Audit config file permissions (SV-270775, 270776, 270777)

chmod 640 /etc/audit/audit.rules /etc/audit/auditd.conf /etc/audit/rules.d/*.rules 2>/dev/null || true
chown root:root /etc/audit/audit.rules /etc/audit/auditd.conf 2>/dev/null || true

journalctl permissions (SV-270758)

chmod 0750 /usr/bin/journalctl

Direct root login (SV-270724)

passwd -l root

FIPS mode (SV-270744)

# CAUTION: on AWS this may break instance connectivity — test on non-production first
apt-get install -y ubuntu-advantage-tools
# ua enable fips-updates  # Requires Ubuntu Pro subscription

Audit rules (abridged)

The remediation script generates the full /etc/audit/rules.d/99-stig.rules. Key groups:

# Identity files
-w /etc/passwd  -p wa -k identity
-w /etc/group   -p wa -k identity
-w /etc/shadow  -p wa -k identity
-w /etc/gshadow -p wa -k identity
-w /etc/opasswd -p wa -k identity

# Privilege escalation
-a always,exit -F arch=b64 -S execve -C uid!=euid -F euid=0 -k setuid
-a always,exit -F arch=b64 -S execve -C gid!=egid -F egid=0 -k setgid

# Sudoers
-w /etc/sudoers         -p wa -k sudoers
-w /etc/sudoers.d/      -p wa -k sudoers

# Module loading
-a always,exit -F arch=b64 -S init_module,finit_module -k modules
-a always,exit -F arch=b64 -S delete_module -k modules

# File attribute changes
-a always,exit -F arch=b64 -S setxattr,fsetxattr,lsetxattr,removexattr,fremovexattr,lremovexattr -k perm_mod
-a always,exit -F arch=b64 -S chown,fchown,fchownat,lchown -k perm_mod
-a always,exit -F arch=b64 -S chmod,fchmod,fchmodat -k perm_mod

# File access
-a always,exit -F arch=b64 -S creat,open,openat,open_by_handle_at,truncate,ftruncate -F exit=-EACCES -k access
-a always,exit -F arch=b64 -S creat,open,openat,open_by_handle_at,truncate,ftruncate -F exit=-EPERM  -k access

# Privileged commands (full list in remediation script)
-a always,exit -F path=/usr/bin/sudo  -F perm=x -k privileged
-a always,exit -F path=/usr/bin/su    -F perm=x -k privileged
-a always,exit -F path=/bin/mount     -F perm=x -k privileged

Anti-patterns

These look like valid hardening moves but will break your instance or produce false-clean scans:

1. Enabling FIPS mode on a running production EC2 instance without a snapshot — ubuntu-advantage-tools FIPS enablement reboots the kernel with FIPS-validated modules. On AWS, if the instance's kernel or init system has dependencies that are absent in FIPS mode, the instance will not come back up. Always snapshot before enabling, and test on a non-production instance first.
2. Using the U_CAN_Ubuntu_24-04_LTS_V1R1 benchmark ID without the full _SCAP_1-3_ path — the SCAP content inside the zip contains multiple component files; passing just the outer zip filename or a truncated path causes --datastream-id lookups to fail silently with a generic Failed to locate a datastream error rather than a helpful message.
3. Running OpenSCAP scan results as the root pass/fail truth without reviewing notapplicable rules — by default OpenSCAP counts notapplicable rules as neutral. On a headless AWS EC2, rules about GUI, removable media, and physical console will all be notapplicable — your real posture score is among fail rules only. Filter the report accordingly.
4. Applying chmod 0750 /usr/bin/journalctl before confirming no monitoring agents use it as a non-root user — this blocks any non-root service (Prometheus node_exporter, Loki Promtail, CloudWatch Agent) from reading journal logs. Fix the permissions on the agent's user first, then apply the STIG rule.
5. Configuring pam_faillock lockout without a console or SSM fallback — if you set deny=3 and the lockout fires on root or ubuntu, you can be permanently locked out of a remote-only instance. Confirm AWS Systems Manager Session Manager is configured and tested before applying PAM lockout rules.
6. Generating AIDE database after the OS is already modified — AIDE's integrity baseline must be generated on a known-good clean state. Running aide --init after applying STIG remediations but before rebooting or before packages are fully settled will bake transient state into the baseline, causing false positives on every subsequent check.
7. Applying audit rules with auditctl -R without reloading auditd — auditctl -R file loads rules for the current session only; they're lost on reboot. Rules must be placed in /etc/audit/rules.d/*.rules and loaded with service auditd restart (or equivalent) to survive reboots and pass the STIG check.

Example prompts

• "How do I run an OpenSCAP SCAP scan on Ubuntu 24.04 with the DISA STIG benchmark?"
• "My scan fails with Failed to locate a datastream. What's the correct benchmark ID?"
• "STIG rule SV-270690 failed — how do I configure PAM lockout after 3 failed attempts?"
• "Which STIG rules should I skip on an AWS EC2 headless instance?"
• "Show me how to configure SSH FIPS 140-3 ciphers for Ubuntu 24.04."
• "Walk me through setting up AIDE integrity monitoring with a daily cron check."
• "I need to pass a DISA STIG audit next week for our EC2 fleet. What do I run first?"

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