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](../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](../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](../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`) | Decision: local-only for now; image not yet forwarding. | auditd enabled and recording locally. **Receiver now deployed** — `serving/audit-collector/` (rsyslog over TCP/514, per-source-host files, DNS name `${AUDIT_HOST}`). **Remaining hardening** — wire the image-side sender (audisp-syslog + rsyslog forward to the host-generic `audit.fleet.lab`, no per-host state); then this row's `rsyslog_remote_loghost` should 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. |

## Things that are NOT deviations (kept / enforced)

- **SELinux enforcing** (`selinux --enforcing`; labels preserved into the erofs).
- **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 — harmless (no interactive
  passwords) and keep the report honest.

## 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).