Files
everything-claude-code/scripts/ci/validate-workflow-security.js
Jamkris cdbc925d89 fix(ci): flag refs/pull checkouts under pull_request_target
The `pull_request_target` rule's `expressionPattern` matches only
the canonical `github.event.pull_request.head.{ref,sha,repo.full_name}`
interpolations. It does not match the second canonical form of
the same exploit — fetching `refs/pull/<N>/{head,merge}` directly:

  - uses: actions/checkout@v4
    with:
      ref: refs/pull/${{ github.event.pull_request.number }}/merge

The merge-ref variant is what GitHub's own security guidance calls
out as the highest-severity privilege-escalation pattern under
`pull_request_target`: it materialises the PR's merge commit
(attacker code spliced with base), executes inside a workflow that
has full repo-scoped tokens, and gives the attacker the chance to
exfiltrate secrets or push to default branches. `refs/pull/N/head`
is functionally equivalent — same source, same trust boundary.

Reproduced on `main` before this commit:

  $ cat /tmp/bad.yml
  name: bad
  on: { pull_request_target: { types: [opened] } }
  permissions: { contents: read }
  jobs:
    do:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v4
          with:
            ref: refs/pull/${{ github.event.pull_request.number }}/merge
            persist-credentials: false
        - run: npm ci --ignore-scripts

  $ ECC_WORKFLOWS_DIR=/tmp node scripts/ci/validate-workflow-security.js
  Validated workflow security for 1 workflow files
  $ echo $?
  0

Expected: violation flagging the refs/pull checkout under pull_request_target.
Actual: passes silently.

Fix: add a `refPattern` to the `pull_request_target` rule:

    /^\s*ref:\s*['"]?[^'"\n]*refs\/(?:remotes\/)?pull\/[^'"\n\s]+/m

and apply it per checkout step inside the existing
event-gated loop. The pattern matches the ref VALUE so it catches
all interpolation shapes — `refs/pull/123/head`,
`refs/pull/${{ github.event.pull_request.number }}/merge`,
`${{ env.FOO }}/refs/pull/N/head` — without enumerating the
possible interpolations themselves.

Scoping: the rule is already gated on the workflow containing
`pull_request_target:`, so non-privileged `pull_request` workflows
that legitimately check out a PR ref are not affected.

After this commit the reproduction above exits 1 with:

  ERROR: bad.yml:10 - pull_request_target must not checkout an untrusted pull_request head ref/repository

Three new regression tests in `tests/ci/validate-workflow-security.test.js`:
  - rejects pull_request_target + refs/pull/<N>/merge
  - rejects pull_request_target + hardcoded refs/pull/<N>/head
  - allows pull_request_target with no `with.ref:` (base-ref checkout —
    the safe pattern from GitHub's own guidance)

Test count: 17 → 20 in this file; full `yarn test` still green.

Together with the previous commit, this closes the two
independent `validate-workflow-security.js` bypasses I found.
2026-05-17 21:19:29 -04:00

257 lines
8.5 KiB
JavaScript

#!/usr/bin/env node
/**
* Reject unsafe GitHub Actions patterns that execute or checkout untrusted PR code
* from privileged events such as workflow_run or pull_request_target.
*/
const fs = require('fs');
const path = require('path');
const DEFAULT_WORKFLOWS_DIR = path.join(__dirname, '../../.github/workflows');
const RULES = [
{
event: 'workflow_run',
eventPattern: /\bworkflow_run\s*:/m,
description: 'workflow_run must not checkout an untrusted workflow_run head ref/repository',
expressionPattern: /\$\{\{\s*github\.event\.workflow_run\.(?:head_branch|head_sha|head_repository(?:\.[A-Za-z0-9_.]+)?)\s*\}\}|\$\{\{\s*github\.event\.workflow_run\.pull_requests\[\d+\]\.head\.(?:ref|sha|repo\.full_name)\s*\}\}/g,
},
{
event: 'pull_request_target',
eventPattern: /\bpull_request_target\s*:/m,
description: 'pull_request_target must not checkout an untrusted pull_request head ref/repository',
expressionPattern: /\$\{\{\s*github\.event\.pull_request\.head\.(?:ref|sha|repo\.full_name)\s*\}\}/g,
// Even without the standard `github.event.pull_request.head.*` expression,
// a checkout under `pull_request_target` that fetches a `refs/pull/<N>/{head,merge}`
// ref pulls attacker-controlled code into a workflow with write-scoped
// tokens. GitHub's security guidance treats both forms equivalently;
// we match the ref value directly so any interpolation that resolves
// to such a ref (`refs/pull/${{ github.event.pull_request.number }}/merge`,
// a hardcoded `refs/pull/123/head`, a `${{ env.X }}` that the maintainer
// assumes is safe, etc.) trips the same rule.
refPattern: /^\s*ref:\s*['"]?[^'"\n]*refs\/(?:remotes\/)?pull\/[^'"\n\s]+/m,
},
];
const WRITE_PERMISSION_PATTERN = /^\s*(?:contents|issues|pull-requests|actions|checks|deployments|discussions|id-token|packages|pages|repository-projects|security-events|statuses):\s*write\b/m;
// `permissions: write-all` is GitHub Actions' shorthand for granting every
// scope write access. The named-scope pattern above misses it because there
// is no scope name on the left of the colon — just the literal `write-all`
// value at the permissions key. Treat both as equivalent for the purposes
// of the persist-credentials and lifecycle-script gates below.
const WRITE_ALL_PATTERN = /^\s*permissions:\s*write-all\b/m;
const NPM_AUDIT_PATTERN = /\bnpm\s+audit\b(?!\s+signatures\b)/;
const NPM_AUDIT_SIGNATURES_PATTERN = /\bnpm\s+audit\s+signatures\b/;
const ACTIONS_CACHE_PATTERN = /uses:\s*['"]?actions\/cache@/m;
const ID_TOKEN_WRITE_PATTERN = /^\s*id-token:\s*write\b/m;
const UNSAFE_INSTALL_PATTERNS = [
{
pattern: /\bnpm\s+ci\b(?![^\n]*--ignore-scripts)/g,
description: 'npm ci must include --ignore-scripts',
},
{
pattern: /\bpnpm\s+install\b(?![^\n]*--ignore-scripts)/g,
description: 'pnpm install must include --ignore-scripts',
},
{
pattern: /\byarn\s+install\b(?![^\n]*--mode=skip-build)/g,
description: 'yarn install must use --mode=skip-build',
},
{
pattern: /\bbun\s+install\b(?![^\n]*--ignore-scripts)/g,
description: 'bun install must include --ignore-scripts',
},
];
function getWorkflowFiles(workflowsDir) {
if (!fs.existsSync(workflowsDir)) {
return [];
}
return fs.readdirSync(workflowsDir)
.filter(file => /\.(?:yml|yaml)$/i.test(file))
.map(file => path.join(workflowsDir, file))
.sort();
}
function getLineNumber(source, index) {
return source.slice(0, index).split(/\r?\n/).length;
}
function extractCheckoutSteps(source) {
const blocks = [];
const lines = source.split(/\r?\n/);
let current = null;
for (let i = 0; i < lines.length; i++) {
const line = lines[i];
const stepStart = line.match(/^(\s*)-\s+/);
if (stepStart) {
if (current) {
blocks.push(current);
}
current = {
indent: stepStart[1].length,
startLine: i + 1,
lines: [line],
};
continue;
}
if (current) {
current.lines.push(line);
}
}
if (current) {
blocks.push(current);
}
return blocks
.map(block => ({
startLine: block.startLine,
text: block.lines.join('\n'),
}))
.filter(block => /uses:\s*['"]?actions\/checkout@/m.test(block.text));
}
function findViolations(filePath, source) {
const violations = [];
const checkoutSteps = extractCheckoutSteps(source);
for (const rule of RULES) {
if (!rule.eventPattern.test(source)) {
continue;
}
for (const step of checkoutSteps) {
for (const match of step.text.matchAll(rule.expressionPattern)) {
violations.push({
filePath,
event: rule.event,
description: rule.description,
expression: match[0],
line: step.startLine + getLineNumber(step.text, match.index) - 1,
});
}
if (rule.refPattern) {
const refMatch = step.text.match(rule.refPattern);
if (refMatch) {
violations.push({
filePath,
event: rule.event,
description: rule.description,
expression: refMatch[0].trim(),
line: step.startLine + getLineNumber(step.text, refMatch.index) - 1,
});
}
}
}
}
if (WRITE_PERMISSION_PATTERN.test(source) || WRITE_ALL_PATTERN.test(source)) {
for (const step of checkoutSteps) {
if (!/persist-credentials:\s*['"]?false['"]?\b/m.test(step.text)) {
violations.push({
filePath,
event: 'write-permission checkout',
description: 'workflows with write permissions must disable checkout credential persistence',
expression: 'actions/checkout without persist-credentials: false',
line: step.startLine,
});
}
}
}
for (const installRule of UNSAFE_INSTALL_PATTERNS) {
for (const match of source.matchAll(installRule.pattern)) {
violations.push({
filePath,
event: 'dependency install scripts',
description: `workflow dependency installs must not run lifecycle scripts: ${installRule.description}`,
expression: match[0],
line: getLineNumber(source, match.index),
});
}
}
if (ID_TOKEN_WRITE_PATTERN.test(source) && ACTIONS_CACHE_PATTERN.test(source)) {
violations.push({
filePath,
event: 'id-token cache',
description: 'workflows with id-token: write must not restore or save shared dependency caches',
expression: 'id-token: write + actions/cache',
line: getLineNumber(source, source.search(ID_TOKEN_WRITE_PATTERN)),
});
}
if (ACTIONS_CACHE_PATTERN.test(source)) {
violations.push({
filePath,
event: 'dependency cache',
description: 'GitHub Actions dependency caches are disabled during active supply-chain hardening',
expression: 'actions/cache',
line: getLineNumber(source, source.search(ACTIONS_CACHE_PATTERN)),
});
}
if (/\bpull_request_target\s*:/m.test(source) && ACTIONS_CACHE_PATTERN.test(source)) {
violations.push({
filePath,
event: 'pull_request_target cache',
description: 'pull_request_target workflows must not restore or save shared dependency caches',
expression: 'pull_request_target + actions/cache',
line: getLineNumber(source, source.search(/\bpull_request_target\s*:/m)),
});
}
if (NPM_AUDIT_PATTERN.test(source) && !NPM_AUDIT_SIGNATURES_PATTERN.test(source)) {
violations.push({
filePath,
event: 'npm audit signatures',
description: 'workflows that run npm audit must also verify registry signatures',
expression: 'npm audit without npm audit signatures',
line: getLineNumber(source, source.search(NPM_AUDIT_PATTERN)),
});
}
return violations;
}
function validateWorkflowSecurity(workflowsDir = DEFAULT_WORKFLOWS_DIR) {
const files = getWorkflowFiles(workflowsDir);
const violations = [];
for (const filePath of files) {
const source = fs.readFileSync(filePath, 'utf8');
violations.push(...findViolations(filePath, source));
}
if (violations.length > 0) {
for (const violation of violations) {
console.error(
`ERROR: ${path.basename(violation.filePath)}:${violation.line} - ${violation.description}`,
);
console.error(` Unsafe expression: ${violation.expression}`);
}
return 1;
}
console.log(`Validated workflow security for ${files.length} workflow files`);
return 0;
}
if (require.main === module) {
process.exit(validateWorkflowSecurity(process.env.ECC_WORKFLOWS_DIR || DEFAULT_WORKFLOWS_DIR));
}
module.exports = {
DEFAULT_WORKFLOWS_DIR,
extractCheckoutSteps,
findViolations,
validateWorkflowSecurity,
};