diskless-workstation/docs/stig-deviations.md

STIG deviation register — diskless fleet image

DISA STIG (SSG xccdf_org.ssgproject.content_profile_stig for RHEL 9) is applied to the image via oscap --remediate with a tailoring file (../files/stig/diskless-tailoring.xml). This register documents every intentional deviation — the rules unselected in that tailoring, plus posture decisions — with the rationale and compensating control. The per-build generated report (stig-deviations.md / stig-report.html, produced by ../scripts/stig-deviations.sh from the post-remediation scan) cross-references this file: any non-pass rule not listed here is flagged REVIEW.

Posture decisions (2026-06-18, lab phase):

• FIPS: OFF — revisit alongside UKI signing / Secure Boot.
• Audit offload: LOCAL-only — auditd runs and logs to the tmpfs overlay; no remote collector yet.
• CI: report-only — oscap eval publishes ARF + HTML; never fails the build.

Intentional deviations

#	STIG/SSG area (rules)	Why it doesn't apply / can't be met	Compensating control
1	Separate partitions + their mount options for /var, /var/log, /var/log/audit, /tmp, /home, /var/tmp, /dev/shm (partition_for_*, mount_option_*)	Root is a single immutable erofs image on NVMe/TCP with a tmpfs volatile overlay — there is no local disk to partition, and these dirs are not separate mounts. The related mount_option_* rules will therefore show as findings; they are covered by this entry.	The entire root is read-only (erofs+dm-verity) and the writable layer is tmpfs (RAM), which structurally bounds the tampering / space-exhaustion risks the partition+option rules target. noexec on /tmp is intentionally NOT forced — the browser kiosk uses /tmp for its profile/cache and can break under noexec.
2	Bootloader / GRUB (grub2_*: password, admin user, and the *_argument kernel-param rules)	Boot is a UKI (systemd-stub) over UEFI HTTP boot — there is no GRUB.	The STIG kernel params (audit=1, audit_backlog_limit, slub_debug=P, page_poison=1, vsyscall=none, init_on_alloc/free) are baked into the signed UKI cmdline (../scripts/extract-artifacts.sh); the cmdline is immutable once signed (Secure Boot covers it), which is stronger than an editable GRUB config.
3	AIDE / file integrity (package_aide_installed, aide_build_database, aide_periodic_cron_checking, aide_scan_notification, aide_verify_*)	The root is read-only and cryptographically verified; an on-disk AIDE db would also be non-deterministic and break the reproducible verity hash.	dm-verity verifies the whole root filesystem against a signed root hash on every read — continuous, hardware-backed integrity that supersedes AIDE's periodic scan.
4	Firewall (service_firewalld_enabled, package_firewalld_installed, set_firewalld_default_zone)	Currently firewall --disabled; auto-enabling firewalld/nftables risks the NVMe/TCP (:4420) and NetworkManager paths during bring-up.	Isolated boot LAN; egress controlled at the serving-stack / network firewall layer. Future hardening — re-enable with explicit allow rules once the secure path is verified.
5	FIPS (enable_fips_mode, grub2_enable_fips_mode, package_dracut-fips_installed)	Decision: off for the lab phase (interacts with the still-unsigned UKI / Secure Boot story).	Revisit with signing. No weakened crypto is configured in the meantime.
6	Remote audit offload (auditd_audispd_configure_remote_server, ..._encrypt_sent_records, ..._network_failure_action, rsyslog_remote_loghost)	The SSG audisp-remote native-protocol rules stay waived; offload is done via rsyslog over TCP instead (simpler, container-friendly receiver). Lab uses plaintext (mirrors the HTTP-boot stack); encryption/failure-action rules remain deviated until TLS/RELP.	Now wired both ends. Sender (image, provisioner 2f, audit_host var): audisp-syslog → LOCAL6 + rsyslog omfwd (disk-assisted queue) to the host-generic audit.fleet.lab. Receiver: serving/audit-collector/ (rsyslog TCP/514, per-source-host files). No per-host state. Future: TLS (gtls) or RELP+TLS + a real collector — then the encrypt/failure-action rules can pass.
7	Smart card login (require_smart_card_login, sssd_enable_smartcard, install_smartcard_packages)	Diskless hosts have no smartcard reader; admin access is SSH key-based. Enforcing smartcard login would lock the host out.	Admin auth is an SSH key-only account; root is locked; password auth disabled.
8	NOPASSWD sudo (sudo_remove_nopasswd)	The baked admin is a passwordless, key-only account, so sudo cannot prompt for a password — NOPASSWD is required for it to function at all.	Single fleet-generic admin, key-only, wheel; no interactive password exists to protect. Tracked for the eventual per-host/rotatable access model (SSH CA / config-agent).
9	GUI / autologin / GDM (gnome screensaver, GDM banner, automatic-login rules)	No GNOME/GDM is installed; the kiosk is an intentional autologin single-app (weston + Chromium) session on kiosk builds.	Kiosk user is unprivileged and passwordless; the session runs a single locked-down browser (no shell, no nav). Applies to kiosk builds only; non-kiosk builds don't install the GUI stack.
10	Password aging / faillock on the key-only APPLIANCE ACCOUNTS (accounts_*_age_*, account_disable_post_pw_expiration, pam_faillock account phase) — applied to the system but exempted for the fleetadmin and kiosk users	These two accounts are passwordless / key-only. The hardened PAM account phase (faillock + password aging/inactivity) treats a passwordless account as expired/lockable, which locked the fleet out: the kiosk autologin session never opened (getty kept tty1) and sshd denied the valid key with Permission denied (publickey) (pubkey auth succeeds, then pam_acct_mgmt fails). Fixed 2026-06-18.	The exemption is scoped to these two appliance accounts only (post-STIG chage -M -1 -m 0 -I -1 -E -1 + faillock --reset; kiosk uses a dedicated /etc/pam.d/kiosk; sshd gets an account sufficient pam_succeed_if.so user = fleetadmin bypass as its first account rule). Every other account keeps the full STIG password policy + faillock. These accounts have no password to age and (key-only, PasswordAuthentication no) no password-auth path for faillock to protect. Folds into the per-host/rotatable access model (SSH CA / config-agent).

| 11 | Login banner content (banner_etc_issue, banner_etc_issue_net, banner_etc_motd) | STIG requires the verbatim DoD/USG "you are accessing a U.S. Government Information System" text. This is a fictional starship fleet, not a USG system, so /etc/issue{,.net} + /etc/motd carry the fleet (ISV AURELIAN) notice instead (provisioner step 2e, files/banner/fleet-issue). The content rules therefore fail by design. | The banner keeps its security function: it still states authorized-crew-only, that the terminal is monitored/logged, and that unauthorized access is prohibited — only the wording is themed. sshd_enable_warning_banner (Banner is shown) still passes. |

Things that are NOT deviations (kept / enforced)

• SELinux enforcing (selinux --enforcing; labels preserved into the erofs).
• fapolicyd kept enabled (NOT waived) — it's the real exec-allowlist guard for the writable RAM overlay, which dm-verity does not cover. The only adjustment: the one non-RPM executable, /usr/local/bin/kiosk-session, is added to fapolicyd's trust DB at build (provisioner 2c-STIG-postfix) so the kiosk runs; everything else stays RPM-trust-only. (fapolicyd blocking that binary was the original kiosk-won't-start cause.)
• auditd enabled; STIG audit rules applied; logs locally.
• sshd hardening: root login off, password & keyboard-interactive auth off, key-only (drop-in 50-fleet-hardening.conf); STIG ciphers/MACs/KEX applied.
• No per-host state: SSH host keys stripped at build, regenerated at first boot into the overlay; machine-id empty.
• Password-policy / faillock rules remain selected and applied system-wide (kept honest in the report); they are exempted only for the two key-only appliance accounts — see deviation #10.

How to read the generated report

scripts/stig-deviations.sh stig-arf.xml emits a table of every rule whose result is not pass. Each row is tagged:

• intentional — matches an unselected rule / area in this register.
• REVIEW — a real finding to triage (fix it, or add a justified entry here).