skip running unsafe pr check if input is default (backport #2518 to releases/v6)

* block checking out fork pr for pull_request_target and workflow_run (#2454)

* block checking out fork pr for some events

* address copilot and reviewer feedback

* run prettier formatting

* build

* update urls

* update readme

* update description and url again

* edit url one more time

* update error wording (#2467)

.github/workflows/publish-immutable-actions.yml

@@ -17,4 +17,4 @@ jobs:
         uses: actions/checkout@v6
       - name: Publish
         id: publish
-        uses: actions/publish-immutable-action@v0.0.4
+        uses: actions/publish-immutable-action@0.0.3

__test__/input-helper.test.ts

@@ -155,4 +155,50 @@ describe('input-helper tests', () => {
     const settings: IGitSourceSettings = await inputHelper.getInputs()
     expect(settings.workflowOrganizationId).toBe(123456)
   })
+
+  describe('unsafe PR checkout guard', () => {
+    const forkPayload = {
+      repository: {id: 100},
+      pull_request: {
+        head: {
+          sha: '1234567890123456789012345678901234567890',
+          repo: {id: 200, full_name: 'attacker/fork'}
+        },
+        merge_commit_sha: 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa'
+      }
+    }
+
+    it('allows the default self-checkout on a fork pull_request_target', async () => {
+      const originalEvent = github.context.eventName
+      const originalPayload = github.context.payload
+      try {
+        github.context.eventName = 'pull_request_target'
+        github.context.payload = forkPayload as any
+        // Simulate a rebase/fast-forward merge where the base tip (event SHA)
+        // equals the PR head SHA. The default self-checkout must still succeed.
+        github.context.sha = '1234567890123456789012345678901234567890'
+        const settings: IGitSourceSettings = await inputHelper.getInputs()
+        expect(settings.commit).toBe('1234567890123456789012345678901234567890')
+      } finally {
+        github.context.eventName = originalEvent
+        github.context.payload = originalPayload
+      }
+    })
+
+    it('refuses an explicit fork repository on pull_request_target', async () => {
+      const originalEvent = github.context.eventName
+      const originalPayload = github.context.payload
+      try {
+        github.context.eventName = 'pull_request_target'
+        github.context.payload = forkPayload as any
+        inputs.repository = 'attacker/fork'
+        await expect(inputHelper.getInputs()).rejects.toThrow(
+          /Refusing to check out fork pull request code/
+        )
+      } finally {
+        github.context.eventName = originalEvent
+        github.context.payload = originalPayload
+      }
+    })
+  })
 })

dist/index.js

@@ -2150,12 +2150,19 @@ function getInputs() {
             (core.getInput('allow-unsafe-pr-checkout') || 'false').toUpperCase() ===
                 'TRUE';
         core.debug(`allow unsafe PR checkout = ${result.allowUnsafePrCheckout}`);
-        unsafePrCheckoutHelper.assertSafePrCheckout({
-            qualifiedRepository,
-            ref: result.ref,
-            commit: result.commit,
-            allowUnsafePrCheckout: result.allowUnsafePrCheckout
-        });
+        // The default self-checkout (this repository with no explicit ref) always
+        // resolves to the trusted ref/commit GitHub set for the triggering event, so
+        // the fork-checkout guard only needs to run when the caller customized the
+        // repository or ref.
+        const isDefaultCheckout = isWorkflowRepository && !core.getInput('ref');
+        if (!isDefaultCheckout) {
+            unsafePrCheckoutHelper.assertSafePrCheckout({
+                qualifiedRepository,
+                ref: result.ref,
+                commit: result.commit,
+                allowUnsafePrCheckout: result.allowUnsafePrCheckout
+            });
+        }
         return result;
     });
 }
@@ -2833,9 +2840,9 @@ function assertSafePrCheckout(input) {
     throw new Error(`Refusing to check out fork pull request code from a '${eventName}' workflow. ` +
         `This workflow runs with the base repository's GITHUB_TOKEN, secrets, default-branch ` +
         `cache scope, and runner access. Fetching and executing a fork's code in that trusted ` +
-        `context commonly leads to "pwn request" vulnerabilities. To opt in after reviewing ` +
-        `the risks at https://gh.io/securely-using-pull_request_target, set ` +
-        `'allow-unsafe-pr-checkout: true' on the actions/checkout step.`);
+        `context commonly leads to "pwn request" vulnerabilities. To opt in, review the risks ` +
+        `at https://gh.io/securely-using-pull_request_target and set 'allow-unsafe-pr-checkout: true' ` +
+        `on the actions/checkout step.`);
 }
 function pushIfSha(target, value) {
     if (typeof value === 'string' && value.length > 0) {

package-lock.json

@@ -28,7 +28,7 @@
         "eslint-plugin-jest": "^28.8.2",
         "jest": "^29.7.0",
         "jest-circus": "^29.7.0",
-        "js-yaml": "^4.2.0",
+        "js-yaml": "^4.1.0",
         "prettier": "^3.3.3",
         "ts-jest": "^29.2.5",
         "typescript": "^5.5.4"
@@ -3590,11 +3590,10 @@
       }
     },
     "node_modules/flatted": {
-      "version": "3.4.2",
-      "resolved": "https://registry.npmjs.org/flatted/-/flatted-3.4.2.tgz",
-      "integrity": "sha512-PjDse7RzhcPkIJwy5t7KPWQSZ9cAbzQXcafsetQoD7sOJRQlGikNbx7yZp2OotDnJyrDcbyRq3Ttb18iYOqkxA==",
-      "dev": true,
-      "license": "ISC"
+      "version": "3.3.1",
+      "resolved": "https://registry.npmjs.org/flatted/-/flatted-3.3.1.tgz",
+      "integrity": "sha512-X8cqMLLie7KsNUDSdzeN8FYK9rEt4Dt67OsG/DNGnYTSDBG4uFAJFBnUeiV+zCVAvwFy56IjM9sH51jVaEhNxw==",
+      "dev": true
     },
     "node_modules/for-each": {
       "version": "0.3.3",
@@ -5187,21 +5186,10 @@
       "license": "MIT"
     },
     "node_modules/js-yaml": {
-      "version": "4.2.0",
-      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-4.2.0.tgz",
-      "integrity": "sha512-ePWsvanv0DWuDRsW8dnt+R4jQ31SCRCQ7hhNcPXZPsoBZiemuZNYGf7adZdqX2D86j6rvKp3RpCxVTSb8WQlOw==",
+      "version": "4.1.0",
+      "resolved": "https://registry.npmjs.org/js-yaml/-/js-yaml-4.1.0.tgz",
+      "integrity": "sha512-wpxZs9NoxZaJESJGIZTyDEaYpl0FKSA+FB9aJiyemKhMwkxQg63h4T1KJgUGHpTqPDNRcmmYLugrRjJlBtWvRA==",
       "dev": true,
-      "funding": [
-        {
-          "type": "github",
-          "url": "https://github.com/sponsors/puzrin"
-        },
-        {
-          "type": "github",
-          "url": "https://github.com/sponsors/nodeca"
-        }
-      ],
-      "license": "MIT",
       "dependencies": {
         "argparse": "^2.0.1"
       },

package.json

@@ -47,7 +47,7 @@
     "eslint-plugin-jest": "^28.8.2",
     "jest": "^29.7.0",
     "jest-circus": "^29.7.0",
-    "js-yaml": "^4.2.0",
+    "js-yaml": "^4.1.0",
     "prettier": "^3.3.3",
     "ts-jest": "^29.2.5",
     "typescript": "^5.5.4"

src/input-helper.ts

@@ -168,12 +168,19 @@ export async function getInputs(): Promise<IGitSourceSettings> {
     'TRUE'
   core.debug(`allow unsafe PR checkout = ${result.allowUnsafePrCheckout}`)
 
-  unsafePrCheckoutHelper.assertSafePrCheckout({
-    qualifiedRepository,
-    ref: result.ref,
-    commit: result.commit,
-    allowUnsafePrCheckout: result.allowUnsafePrCheckout
-  })
+  // The default self-checkout (this repository with no explicit ref) always
+  // resolves to the trusted ref/commit GitHub set for the triggering event, so
+  // the fork-checkout guard only needs to run when the caller customized the
+  // repository or ref.
+  const isDefaultCheckout = isWorkflowRepository && !core.getInput('ref')
+  if (!isDefaultCheckout) {
+    unsafePrCheckoutHelper.assertSafePrCheckout({
+      qualifiedRepository,
+      ref: result.ref,
+      commit: result.commit,
+      allowUnsafePrCheckout: result.allowUnsafePrCheckout
+    })
+  }
 
   return result
 }

src/unsafe-pr-checkout-helper.ts

@@ -75,9 +75,9 @@ export function assertSafePrCheckout(input: IUnsafePrCheckoutInput): void {
     `Refusing to check out fork pull request code from a '${eventName}' workflow. ` +
       `This workflow runs with the base repository's GITHUB_TOKEN, secrets, default-branch ` +
       `cache scope, and runner access. Fetching and executing a fork's code in that trusted ` +
-      `context commonly leads to "pwn request" vulnerabilities. To opt in after reviewing ` +
-      `the risks at https://gh.io/securely-using-pull_request_target, set ` +
-      `'allow-unsafe-pr-checkout: true' on the actions/checkout step.`
+      `context commonly leads to "pwn request" vulnerabilities. To opt in, review the risks ` +
+      `at https://gh.io/securely-using-pull_request_target and set 'allow-unsafe-pr-checkout: true' ` +
+      `on the actions/checkout step.`
   )
 }