approval-engine/docs/image-scan-2026-09-06.md

# Image scan — 2026-09-06

Scanner: `aquasec/trivy:latest` (`--scanners vuln`), run against locally built
images. Requested by `glas-harness` under `GLAS-WP-0015` / `APPROVAL-WP-0002-T03`.

**No image was pushed.** The scan is why — see "Why nothing was released".

## Results

| Image | CRITICAL | HIGH | MEDIUM |
| --- | --- | --- | --- |
| As pinned before this session (`python:3.12-slim@sha256:d764629c…`, Debian 13.5) | 3 | 81 | 103 |
| `slim-hardened` — base bumped to `@sha256:78387bc3…` (Debian 13.6), pip removed | 3 | 51 | 56 |
| `alpine` — `python:3.12-alpine@sha256:b64631e0…` (Alpine 3.24.1), pip removed | **0** | **7** | **1** |

Every finding is inherited from the base image or its distro packages. None is in
`approval_engine` code, and after removing pip the Python dependency layer
(`cryptography` 50.0.1, `PyJWT` 2.13.0, `waitress` 3.0.2, `cffi`, `pycparser`)
reports zero findings at MEDIUM and above in all three.

## Two fixes applied

**The base pin was stale.** `Containerfile` pinned a Debian 13.5 build of
`python:3.12-slim`; current upstream is Debian 13.6. Bumping the pin removes 30
HIGH and 47 MEDIUM findings on its own. The pin is still a digest, not a tag —
the fix is a newer immutable pin, not a floating one.

**pip is gone from the runtime image.** All 10 MEDIUM Python findings were in
pip itself, which is a build-time tool with no business in a running approval
service. The build is now two-stage: pip installs the venv in the build stage
and is deleted from both the venv and the base's `/usr/local` in the runtime
stage. `command -v pip pip3 pip3.12` returns nothing in both variants.

## The three CRITICALs, and why the base choice is now open

The remaining CRITICALs on Debian are all `perl-base` 5.40.1-6:

- `CVE-2026-13221`
- `CVE-2026-42496`
- `CVE-2026-8376`

**All three have no upstream fix** (trivy reports no fixed version), so no base
bump or package upgrade clears them. `perl-base` is `Essential: yes` on Debian
and is not safely removable. This service does not use perl at any point.

Alpine carries no perl at all, which is why it reports 0 CRITICAL. That makes
the base a real decision rather than a preference:

- **Alpine** clears all three CRITICALs and drops HIGH from 51 to 7, but changes
  the C library from glibc to musl.
- **Debian slim** keeps glibc and ships three unfixable CRITICALs in a package
  the service never calls.

### Evidence that Alpine is viable

- Image builds with no compiler toolchain: `cryptography` 50.0.1 installs from
  musllinux wheels.
- **The full test suite passes on musl: 111 passed**, the same count as the
  workstation. (An earlier run showed 102 passed / 1 skipped; the 9-test gap was
  `tests/test_examples.py` skipping on a missing `jsonschema` test dependency in
  the throwaway container, not a musl failure.)
- Runtime identity `uid=10001(approval) gid=10001(approval)`, non-root.
- Carries `LATEST_SCHEMA_VERSION = 3` and `Engine` tenant default
  `tenant:platform`.
- First-install migration on a fresh volume: `migrate` then `verify` both report
  `schema_version: 3`, `schema_current: true`, `integrity: ["ok"]`,
  `foreign_key_violations: 0`, `persistent: true`.
- Fail-closed gates hold in the image: `serve --production --db :memory:`
  refuses with "production requires a persistent database"; production without
  audit configuration refuses with "production requires authenticated audit
  delivery".

`Containerfile.alpine` holds this variant. It is a **candidate**, not the
sanctioned base — the sanctioned base is still `Containerfile`.

## Why nothing was released

`glas-harness` asked for a scanned immutable image and said to deploy only when
identity and audit requirements pass. The scan gate is not met by the Debian
variant, and pushing it would bake three unfixable CRITICALs into a release
digest that the manifest then pins by hash.

Choosing the runtime C library for a production approval service is also not a
call this repo should make silently. So:

- No push to `forgejo.coulomb.social`.
- `deploy/approval-engine.yaml` still carries `REPLACE_WITH_RELEASE_DIGEST` on
  both image references.
- `APPROVAL-WP-0002-T03` stays `wait`.

Local build digests, recorded for traceability and explicitly **not** release
digests: `slim-hardened` `sha256:78b87e68e520…`, `alpine` `sha256:736647294706…`.

## Open questions for owners

1. Is Alpine/musl acceptable as the sanctioned base for this service? If yes,
   `Containerfile.alpine` becomes `Containerfile` and the release is scanned
   clean of CRITICALs.
2. If glibc is required, is a documented exception for the three unfixable
   `perl-base` CVEs acceptable, given the service never invokes perl? A
   distroless glibc base is the third option and was not evaluated here.
3. Which scanner is sanctioned for the gate? This used trivy because it needed
   no install; the estate may have a different standard.