Merge 2d76d21b2e into 62661c4e71

configureTempGlobalConfig isolates global git config by overriding HOME to
a temporary directory. But GIT_CONFIG_GLOBAL takes precedence over HOME when
git locates the global config file, so when a workflow already has
GIT_CONFIG_GLOBAL set in the environment, 'git config --global' writes land
in that file instead of the temporary config. replaceTokenPlaceholder then
reads the temporary config, cannot find the placeholder, and fails with
'Unable to replace auth placeholder'.

Set GIT_CONFIG_GLOBAL to the temporary config alongside the HOME override so
global config operations always target the temp file regardless of any
inherited value, and unset it again in removeGlobalConfig.

Assisted-By: Claude Opus 4.8

__test__/git-auth-helper.test.ts

@@ -923,6 +923,25 @@ describe('git-auth-helper tests', () => {
     }
   })
 
+  const configureGlobalAuth_overridesGitConfigGlobal =
+    'configureGlobalAuth overrides GIT_CONFIG_GLOBAL'
+  it(configureGlobalAuth_overridesGitConfigGlobal, async () => {
+    // Arrange
+    await setup(configureGlobalAuth_overridesGitConfigGlobal)
+    const authHelper = gitAuthHelper.createAuthHelper(git, settings)
+
+    // Act
+    await authHelper.configureAuth()
+    await authHelper.configureGlobalAuth()
+
+    // Assert GIT_CONFIG_GLOBAL is pinned to the temporary global config, so an
+    // inherited GIT_CONFIG_GLOBAL cannot redirect --global writes
+    expect(git.env['HOME']).toBeTruthy()
+    expect(git.env['GIT_CONFIG_GLOBAL']).toBe(
+      path.join(git.env['HOME'], '.gitconfig')
+    )
+  })
+
   const removeGlobalConfig_removesOverride =
     'removeGlobalConfig removes override'
   it(removeGlobalConfig_removesOverride, async () => {
@@ -933,6 +952,7 @@ describe('git-auth-helper tests', () => {
     await authHelper.configureGlobalAuth()
     const homeOverride = git.env['HOME'] // Sanity check
     expect(homeOverride).toBeTruthy()
+    expect(git.env['GIT_CONFIG_GLOBAL']).toBeTruthy()
     await fs.promises.stat(path.join(git.env['HOME'], '.gitconfig'))
 
     // Act
@@ -940,6 +960,7 @@ describe('git-auth-helper tests', () => {
 
     // Assert
     expect(git.env['HOME']).toBeUndefined()
+    expect(git.env['GIT_CONFIG_GLOBAL']).toBeUndefined()
     try {
       await fs.promises.stat(homeOverride)
       throw new Error(`Should have been deleted '${homeOverride}'`)

__test__/input-helper.test.ts

@@ -180,4 +180,50 @@ 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 = mockGithubContext.eventName
+      const originalPayload = mockGithubContext.payload
+      try {
+        mockGithubContext.eventName = 'pull_request_target'
+        mockGithubContext.payload = forkPayload
+        // Simulate a rebase/fast-forward merge where the base tip (event SHA)
+        // equals the PR head SHA. The default self-checkout must still succeed.
+        mockGithubContext.sha = '1234567890123456789012345678901234567890'
+        const settings: IGitSourceSettings = await inputHelper.getInputs()
+        expect(settings.commit).toBe('1234567890123456789012345678901234567890')
+      } finally {
+        mockGithubContext.eventName = originalEvent
+        mockGithubContext.payload = originalPayload
+      }
+    })
+
+    it('refuses an explicit fork repository on pull_request_target', async () => {
+      const originalEvent = mockGithubContext.eventName
+      const originalPayload = mockGithubContext.payload
+      try {
+        mockGithubContext.eventName = 'pull_request_target'
+        mockGithubContext.payload = forkPayload
+        inputs.repository = 'attacker/fork'
+        await expect(inputHelper.getInputs()).rejects.toThrow(
+          /Refusing to check out fork pull request code/
+        )
+      } finally {
+        mockGithubContext.eventName = originalEvent
+        mockGithubContext.payload = originalPayload
+      }
+    })
+  })
 })

dist/index.js

@@ -35109,6 +35109,10 @@ class GitAuthHelper {
         // Override HOME
         info(`Temporarily overriding HOME='${this.temporaryHomePath}' before making global git config changes`);
         this.git.setEnvironmentVariable('HOME', this.temporaryHomePath);
+        // GIT_CONFIG_GLOBAL takes precedence over HOME when locating the global
+        // config file. Pin it to the temporary config so an inherited
+        // GIT_CONFIG_GLOBAL cannot redirect our global git config writes elsewhere.
+        this.git.setEnvironmentVariable('GIT_CONFIG_GLOBAL', newGitConfigPath);
         return newGitConfigPath;
     }
     async configureGlobalAuth() {
@@ -35183,8 +35187,9 @@ class GitAuthHelper {
     }
     async removeGlobalConfig() {
         if (this.temporaryHomePath?.length > 0) {
-            core_debug(`Unsetting HOME override`);
+            core_debug(`Unsetting HOME and GIT_CONFIG_GLOBAL overrides`);
             this.git.removeEnvironmentVariable('HOME');
+            this.git.removeEnvironmentVariable('GIT_CONFIG_GLOBAL');
             await rmRF(this.temporaryHomePath);
         }
     }
@@ -42191,12 +42196,19 @@ async function getInputs() {
         (getInput('allow-unsafe-pr-checkout') || 'false').toUpperCase() ===
             'TRUE';
     core_debug(`allow unsafe PR checkout = ${result.allowUnsafePrCheckout}`);
-    assertSafePrCheckout({
+    // The default self-checkout (this repository with no explicit ref) always
-        qualifiedRepository,
+    // resolves to the trusted ref/commit GitHub set for the triggering event, so
-        ref: result.ref,
+    // the fork-checkout guard only needs to run when the caller customized the
-        commit: result.commit,
+    // repository or ref.
-        allowUnsafePrCheckout: result.allowUnsafePrCheckout
+    const isDefaultCheckout = isWorkflowRepository && !getInput('ref');
-    });
+    if (!isDefaultCheckout) {
+        assertSafePrCheckout({
+            qualifiedRepository,
+            ref: result.ref,
+            commit: result.commit,
+            allowUnsafePrCheckout: result.allowUnsafePrCheckout
+        });
+    }
     return result;
 }
 

src/git-auth-helper.ts

@@ -122,6 +122,11 @@ class GitAuthHelper {
     )
     this.git.setEnvironmentVariable('HOME', this.temporaryHomePath)
 
+    // GIT_CONFIG_GLOBAL takes precedence over HOME when locating the global
+    // config file. Pin it to the temporary config so an inherited
+    // GIT_CONFIG_GLOBAL cannot redirect our global git config writes elsewhere.
+    this.git.setEnvironmentVariable('GIT_CONFIG_GLOBAL', newGitConfigPath)
+
     return newGitConfigPath
   }
 
@@ -237,8 +242,9 @@ class GitAuthHelper {
 
   async removeGlobalConfig(): Promise<void> {
     if (this.temporaryHomePath?.length > 0) {
-      core.debug(`Unsetting HOME override`)
+      core.debug(`Unsetting HOME and GIT_CONFIG_GLOBAL overrides`)
       this.git.removeEnvironmentVariable('HOME')
+      this.git.removeEnvironmentVariable('GIT_CONFIG_GLOBAL')
       await io.rmRF(this.temporaryHomePath)
     }
   }

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({
+  // The default self-checkout (this repository with no explicit ref) always
-    qualifiedRepository,
+  // resolves to the trusted ref/commit GitHub set for the triggering event, so
-    ref: result.ref,
+  // the fork-checkout guard only needs to run when the caller customized the
-    commit: result.commit,
+  // repository or ref.
-    allowUnsafePrCheckout: result.allowUnsafePrCheckout
+  const isDefaultCheckout = isWorkflowRepository && !core.getInput('ref')
-  })
+  if (!isDefaultCheckout) {
+    unsafePrCheckoutHelper.assertSafePrCheckout({
+      qualifiedRepository,
+      ref: result.ref,
+      commit: result.commit,
+      allowUnsafePrCheckout: result.allowUnsafePrCheckout
+    })
+  }
 
   return result
 }