ci: actions by commit, govulncheck, images pinned, base packages watched (audit I4, I5)

Security audit 2026-10-17, findings I4 and I5 (low), stage 5.

I4: every action is pinned by commit with its version in a comment - the
latest release of the major each used, so nothing changes in behaviour
(checkout v4.4.0, setup-go v5.6.0, setup-buildx-action v3.12.0,
build-push-action v6.19.2, login-action v3.7.0; commits read with git
ls-remote, the tags are lightweight). govulncheck v1.9.0 runs on the
source in test.yml, and in release.yml on the image's panel and
selfpost-backup binaries before the push (-mode=binary: the base image's
Go, which may lag the runner's - a fixed stdlib advisory then fails the
release until golang:1.26-trixie moves, which is the point). certbot is
pinned to v5.8.0 and Caddy to 2.11.7 (Docker Hub, 2026-10-17).
provenance/SBOM stay off until the GHCR cleanup keeps attestations, as the
plan says.

I5: published tags are never rebuilt, so a Debian security fix reaches
operators with the next release. The guide (§ Upgrading) and SECURITY.md
say so; base-packages.yml runs .github/scripts/base-packages.sh every
Monday: what debian:trixie-slim would install for postfix, libsasl2-2,
libsasl2-modules-db, sasl2-bin, openssl, libssl3t64, libdb5.3t64 against
the table in development.md (the 2.14.3 image's versions), red when one
moved. Tried on the test server: green as it stands, red with a version
changed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/scripts/base-packages.sh

@@ -0,0 +1,32 @@
+#!/bin/sh
+# base-packages.sh: compare the Debian packages the mail path runs on with
+# what debian:trixie-slim would install today (security audit 2026-10-17,
+# I5). The image installs without pinning, and published tags are never
+# rebuilt, so a security update of postfix, Cyrus SASL, OpenSSL or Berkeley
+# DB reaches operators only with the next release. This fails when one of
+# them has moved past the version the last release was built with - the
+# table between the base-package-versions markers in docs/development.md -
+# as the nudge to cut a patch release (and then to update the table).
+#
+# Run by .github/workflows/base-packages.yml every week; needs docker.
+set -eu
+doc=docs/development.md
+table=$(sed -n '/<!-- base-package-versions -->/,/<!-- \/base-package-versions -->/p' "$doc" |
+	sed -n 's/^| `\([^`]*\)` | `\([^`]*\)` |$/\1 \2/p')
+[ -n "$table" ] || { echo "no base-package-versions table in $doc" >&2; exit 2; }
+names=$(echo "$table" | cut -d' ' -f1 | tr '\n' ' ')
+# apt-cache policy's "Candidate:" is what an install would take now.
+now=$(docker run --rm debian:trixie-slim sh -c "apt-get update -qq >/dev/null && for p in $names; do printf '%s %s\n' \"\$p\" \"\$(apt-cache policy \"\$p\" | sed -n 's/^ *Candidate: //p')\"; done")
+moved=0
+echo "$table" | while read -r name built; do
+	cand=$(echo "$now" | awk -v n="$name" '$1 == n { print $2 }')
+	if [ "$cand" != "$built" ]; then
+		echo "::warning::$name: the last release was built with $built, trixie now installs ${cand:-nothing}" >&2
+		echo moved
+	fi
+done | grep -q moved && moved=1
+if [ "$moved" = 1 ]; then
+	echo "A package the mail path runs on has moved: cut a patch release, then update the table in $doc." >&2
+	exit 1
+fi
+echo "Every watched package is as the last release was built."

.github/workflows/base-packages.yml

@@ -0,0 +1,20 @@
+name: base packages
+
+# Every Monday: has a Debian package the mail path runs on moved since the
+# last release was built? A red run is the nudge to cut a patch release
+# (security audit 2026-10-17, I5; .github/scripts/base-packages.sh).
+on:
+  schedule:
+    - cron: "17 5 * * 1"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  watch:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
+      - name: Compare with trixie
+        run: sh .github/scripts/base-packages.sh

.github/workflows/release.yml

@@ -66,14 +66,14 @@ jobs:
             arch: arm64
     runs-on: ${{ matrix.runner }}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
         with:
           ref: v${{ needs.prepare.outputs.version }}
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3.12.0
 
       - name: Build image (native, loaded locally for the e2e gate)
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@10e90e3645eae34f1e60eeb005ba3a3d33f178e8 # v6.19.2
         with:
           context: .
           file: build/Dockerfile
@@ -83,7 +83,7 @@ jobs:
             VERSION=${{ needs.prepare.outputs.version }}
           tags: selfpost:e2e
 
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff # v5.6.0
         with:
           go-version: "1.26"
           cache-dependency-path: test/e2e/go.sum
@@ -110,8 +110,22 @@ jobs:
             fi
           done
 
+      # The binaries about to be pushed, as built in the image - with the Go
+      # of golang:1.26-trixie, which may lag the runner's: a standard-library
+      # advisory fixed in a later patch fails the release until the base tag
+      # moves, which is the point (security audit 2026-10-17, I4).
+      - name: Vulnerabilities in the image's binaries
+        run: |
+          set -euo pipefail
+          id=$(docker create selfpost:e2e)
+          trap 'docker rm -f "$id" >/dev/null' EXIT
+          for bin in panel selfpost-backup; do
+            docker cp "$id:/usr/local/bin/$bin" "/tmp/$bin"
+            go run golang.org/x/vuln/cmd/govulncheck@v1.9.0 -mode=binary "/tmp/$bin"
+          done
+
       - name: Log in to ghcr.io
-        uses: docker/login-action@v3
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3.7.0
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
@@ -152,14 +166,14 @@ jobs:
     needs: [prepare, build]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
         with:
           ref: v${{ needs.prepare.outputs.version }}
 
-      - uses: docker/setup-buildx-action@v3
+      - uses: docker/setup-buildx-action@8d2750c68a42422c14e847fe6c8ac0403b4cbd6f # v3.12.0
 
       - name: Log in to ghcr.io
-        uses: docker/login-action@v3
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3.7.0
         with:
           registry: ghcr.io
           username: ${{ github.actor }}

.github/workflows/test.yml

@@ -9,7 +9,7 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
         with:
           # design-first.sh reads each commit's parent and the template history.
           fetch-depth: 0
@@ -20,7 +20,7 @@ jobs:
           HEAD: ${{ github.event.pull_request.head.sha || github.sha }}
         run: bash .github/scripts/design-first.sh "$BASE" "$HEAD"
 
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff # v5.6.0
         with:
           go-version: "1.26"
           cache: true
@@ -51,6 +51,13 @@ jobs:
       - name: Test
         run: go test ./...
 
+      # Known vulnerabilities in the module's dependencies and in the
+      # standard library of this Go, reached from SelfPost's code (security
+      # audit 2026-10-17, I4: twelve stdlib advisories went unnoticed until
+      # the base image's tag happened to move). Pinned like staticcheck.
+      - name: Vulnerabilities
+        run: go run golang.org/x/vuln/cmd/govulncheck@v1.9.0 ./...
+
       # The e2e module runs only in release.yml, after a release is published;
       # a type error there would first show up then. Compile it here without
       # running it: `go test -run` would still run TestMain, which brings up