fix: enforce allowed-account-ids on all auth paths (#1847)

* fix: enforce allowed-account-ids on all auth paths

The allowed-account-ids list was only enforced in some auth flows. This
was due to the check being included in validateCredentials, which was
skipped if (GITHUB_ACTIONS && AccessKeyId && output-env-credentials) ->
false.

This unifies credential validation into a single path.

- validateCredentials(credentials?, ...) resolves credentials, proves
  liveness via one GetCallerIdentity call, and returns the identity.
- validateAccountId(expectedAccountIds, account) is now a pure comparison
  against the resolved account, enforced against the final (assumed)
  account independent of auth method, GITHUB_ACTIONS, or
  output-env-credentials.
- exportAccountId(identity, ...) consumes the resolved identity instead of
  making its own GetCallerIdentity call, so credential resolution happens
  exactly once per credential set.

Pre-assume account checks remain gated on !roleToAssume so cross-account
assume-role (source account differs from the role's target) is preserved.

Adds regression tests for the OIDC wrong-account case (the previously
missing negative test), OIDC with output-env-credentials: false, and the
assume-role wrong-account case.

* chore: move validateAccountId into helpers

README.md

@@ -776,7 +776,10 @@ the environment (for example, on a self-hosted runner where you do not want the
 assumed-role credentials to shadow an existing EC2 instance profile), pair
 `output-credentials: true` with `output-env-credentials: false`. In that mode,
 the action does not run its post-credential SDK-pickup validation step, since
-the credentials were never written to the environment.
+the credentials were never written to the environment. The action still
+validates the resolved credentials by calling `sts:GetCallerIdentity` with the
+explicit credentials, so the `allowed-account-ids` check can be enforced if
+provided.
 
 ### Configure multiple AWS profiles in a single workflow
 

src/CredentialsClient.ts

@@ -53,54 +53,55 @@ export class CredentialsClient {
 
   public get stsClient(): STSClient {
     if (!this._stsClient || this.roleChaining) {
-      this._stsClient = new STSClient({
-        customUserAgent: buildCustomUserAgent(),
-        ...(this.region !== undefined && { region: this.region }),
-        ...(this.stsEndpoint !== undefined && { endpoint: this.stsEndpoint }),
-        ...(this.requestHandler !== undefined && { requestHandler: this.requestHandler }),
-      });
+      this._stsClient = this.createStsClient();
     }
     return this._stsClient;
   }
 
+  // Builds an STS client using the action's configured region/endpoint/proxy. When explicit credentials are provided,
+  // the client uses them directly instead of the SDK default credential provider chain.
+  // This matters for validateAccountId.
+  private createStsClient(credentials?: AwsCredentialIdentity): STSClient {
+    return new STSClient({
+      customUserAgent: buildCustomUserAgent(),
+      ...(this.region !== undefined && { region: this.region }),
+      ...(this.stsEndpoint !== undefined && { endpoint: this.stsEndpoint }),
+      ...(this.requestHandler !== undefined && { requestHandler: this.requestHandler }),
+      ...(credentials !== undefined && { credentials }),
+    });
+  }
+
+  // Validates that the credentials the action will hand to subsequent steps actually work, and returns the resolved
+  // caller identity (account + ARN). "Work" is proven by a sts:GetCallerIdentity call, which both confirms the
+  // credentials are accepted by AWS and returns the identity for later checks and outputs to use.
   public async validateCredentials(
+    credentials?: AwsCredentialIdentity,
     expectedAccessKeyId?: string,
     roleChaining?: boolean,
-    expectedAccountIds?: string[],
-  ) {
-    let credentials: AwsCredentialIdentity;
-    try {
-      credentials = await this.loadCredentials();
-      if (!credentials.accessKeyId) {
-        throw new Error('Access key ID empty after loading credentials');
-      }
-    } catch (error) {
-      throw new Error(`Credentials could not be loaded, please check your action inputs: ${errorMessage(error)}`);
-    }
-    if (expectedAccountIds && expectedAccountIds.length > 0 && expectedAccountIds[0] !== '') {
-      let callerIdentity: Awaited<ReturnType<typeof getCallerIdentity>>;
+  ): Promise<Awaited<ReturnType<typeof getCallerIdentity>>> {
+    if (!credentials) {
+      let resolved: AwsCredentialIdentity;
       try {
-        callerIdentity = await getCallerIdentity(this.stsClient);
+        resolved = await this.loadCredentials();
+        if (!resolved.accessKeyId) {
+          throw new Error('Access key ID empty after loading credentials');
+        }
       } catch (error) {
-        throw new Error(`Could not validate account ID of credentials: ${errorMessage(error)}`);
+        throw new Error(`Credentials could not be loaded, please check your action inputs: ${errorMessage(error)}`);
       }
-      if (!callerIdentity.Account || !expectedAccountIds.includes(callerIdentity.Account)) {
-        throw new Error(
-          `The account ID of the provided credentials (${
-            callerIdentity.Account ?? 'unknown'
-          }) does not match any of the expected account IDs: ${expectedAccountIds.join(', ')}`,
-        );
-      }
-    }
-
-    if (!roleChaining) {
-      const actualAccessKeyId = credentials.accessKeyId;
-      if (expectedAccessKeyId && expectedAccessKeyId !== actualAccessKeyId) {
+      if (!roleChaining && expectedAccessKeyId && expectedAccessKeyId !== resolved.accessKeyId) {
         throw new Error(
           'Credentials loaded by the SDK do not match the expected access key ID configured by the action',
         );
       }
     }
+
+    const client = credentials ? this.createStsClient(credentials) : this.stsClient;
+    try {
+      return await getCallerIdentity(client);
+    } catch (error) {
+      throw new Error(`Credentials could not be loaded, please check your action inputs: ${errorMessage(error)}`);
+    }
   }
 
   private async loadCredentials() {

src/helpers.ts

@@ -3,6 +3,7 @@ import * as path from 'node:path';
 import * as core from '@actions/core';
 import type { Credentials, STSClient } from '@aws-sdk/client-sts';
 import { GetCallerIdentityCommand } from '@aws-sdk/client-sts';
+import type { AwsCredentialIdentity } from '@aws-sdk/types';
 import type { UserAgent } from '@smithy/types';
 import type { CredentialsClient } from './CredentialsClient';
 
@@ -150,9 +151,8 @@ export async function getCallerIdentity(client: STSClient): Promise<{ Account: s
   return result;
 }
 
-// Obtains account ID from STS Client and sets it as output
-export async function exportAccountId(credentialsClient: CredentialsClient, maskAccountId?: boolean) {
-  const identity = await getCallerIdentity(credentialsClient.stsClient);
+// Emits the account ID and ARN of an already-resolved caller identity as action outputs.
+export function exportAccountId(identity: { Account: string; Arn: string }, maskAccountId?: boolean) {
   const accountId = identity.Account;
   const arn = identity.Arn;
   if (maskAccountId) {
@@ -164,6 +164,35 @@ export async function exportAccountId(credentialsClient: CredentialsClient, mask
   return accountId;
 }
 
+// Validates that the account of the already-resolved caller identity is in the allow-list provided via the
+// `allowed-account-ids` input.
+export function validateAccountId(expectedAccountIds: string[] | undefined, account: string | undefined): void {
+  if (!expectedAccountIds || expectedAccountIds.length === 0 || expectedAccountIds[0] === '') {
+    return;
+  }
+  if (!account || !expectedAccountIds.includes(account)) {
+    throw new Error(
+      `The account ID of the provided credentials (${
+        account ?? 'unknown'
+      }) does not match any of the expected account IDs: ${expectedAccountIds.join(', ')}`,
+    );
+  }
+}
+
+// Converts the STS Credentials shape (returned by AssumeRole and provided as action inputs) into
+// the AwsCredentialIdentity shape the SDK expects when credentials are supplied explicitly to a
+// client. Returns undefined if the access key ID or secret access key is missing.
+export function toCredentialIdentity(creds?: Partial<Credentials>): AwsCredentialIdentity | undefined {
+  if (!creds?.AccessKeyId || !creds.SecretAccessKey) {
+    return undefined;
+  }
+  return {
+    accessKeyId: creds.AccessKeyId,
+    secretAccessKey: creds.SecretAccessKey,
+    ...(creds.SessionToken && { sessionToken: creds.SessionToken }),
+  };
+}
+
 // Tags have a more restrictive set of acceptable characters than GitHub environment variables can.
 // This replaces anything not conforming to the tag restrictions by inverting the regular expression.
 // See the AWS documentation for constraint specifics https://docs.aws.amazon.com/STS/latest/APIReference/API_Tag.html.

src/index.ts

@@ -10,8 +10,10 @@ import {
   exportRegion,
   getBooleanInput,
   retryAndBackoff,
+  toCredentialIdentity,
   translateEnvVariables,
   unsetCredentials,
+  validateAccountId,
   verifyKeys,
 } from './helpers';
 import { writeProfileFiles } from './profileManager';
@@ -51,8 +53,8 @@ export async function run() {
     });
     const roleChaining = getBooleanInput('role-chaining', { required: false });
     const outputCredentials = getBooleanInput('output-credentials', { required: false });
-    // Default to always outputting environment credentials unless profile is specified. If profile is specified, default to
-    // no environment credentials (but still output them if the user specifically requests it).
+    // Default to always outputting environment credentials unless profile is specified. If profile is specified, default
+    // to no environment credentials (but still output them if the user specifically requests it).
     const outputEnvCredentials = getBooleanInput('output-env-credentials', { required: false, default: !awsProfile });
     const unsetCurrentCredentials = getBooleanInput('unset-current-credentials', { required: false });
     let disableRetry = getBooleanInput('disable-retry', { required: false });
@@ -198,27 +200,38 @@ export async function run() {
         writeProfileFiles(awsProfile, { AccessKeyId, SecretAccessKey, SessionToken }, region, overwriteAwsProfile);
       }
     } else if (!webIdentityTokenFile && !roleChaining) {
-      // Proceed only if credentials can be picked up
-      await withRetry(
-        () => credentialsClient.validateCredentials(undefined, roleChaining, expectedAccountIds),
+      // Proceed only if credentials can be picked up. validateCredentials resolves the ambient
+      // credentials via the SDK default chain, proves they work, and returns the caller identity.
+      const identity = await withRetry(
+        () => credentialsClient.validateCredentials(undefined, undefined, roleChaining),
         'validateCredentials',
       );
-      sourceAccountId = await withRetry(() => exportAccountId(credentialsClient, maskAccountId), 'exportAccountId');
+      // Enforce the allowed-account-ids guardrail unless a role will be assumed, in which case the
+      // final account is validated after assumeRole (these ambient credentials are the source account).
+      if (!roleToAssume) {
+        validateAccountId(expectedAccountIds, identity.Account);
+      }
+      sourceAccountId = exportAccountId(identity, maskAccountId);
     }
 
     if (AccessKeyId || roleChaining) {
-      // Validate that the SDK can actually pick up credentials.
-      // This validates cases where this action is using existing environment credentials,
-      // and cases where the user intended to provide input credentials but the secrets inputs resolved to empty strings.
-      // Skip when output-env-credentials is false: input IAM keys were not written to env, so
-      // the default chain would resolve to ambient runner credentials and the access-key check
-      // would spuriously fail (see #1554).
+      // Validate that the credentials the action will use actually work, and resolve their identity.
+      const resolutionCredentials =
+        outputEnvCredentials || !AccessKeyId
+          ? undefined
+          : toCredentialIdentity({ AccessKeyId, SecretAccessKey, SessionToken });
+      const identity = await withRetry(
+        () => credentialsClient.validateCredentials(resolutionCredentials, AccessKeyId, roleChaining),
+        'validateCredentials',
+      );
+      // Enforce the allowed-account-ids guardrail unless a role will be assumed (the final account is
+      // validated after assumeRole; these are the source credentials).
+      if (!roleToAssume) {
+        validateAccountId(expectedAccountIds, identity.Account);
+      }
+      sourceAccountId = identity.Account;
       if (outputEnvCredentials) {
-        await withRetry(
-          () => credentialsClient.validateCredentials(AccessKeyId, roleChaining, expectedAccountIds),
-          'validateCredentials',
-        );
-        sourceAccountId = await withRetry(() => exportAccountId(credentialsClient, maskAccountId), 'exportAccountId');
+        exportAccountId(identity, maskAccountId);
       }
     }
     if (customTags && (useGitHubOIDCProvider() || webIdentityTokenFile)) {
@@ -252,24 +265,15 @@ export async function run() {
       } while (specialCharacterWorkaround && !verifyKeys(roleCredentials.Credentials));
       core.info(`Authenticated as assumedRoleId ${roleCredentials.AssumedRoleUser?.AssumedRoleId}`);
       exportCredentials(roleCredentials.Credentials, outputCredentials, outputEnvCredentials);
-      // Validate that the SDK can pick up the assumed-role credentials from the environment.
-      // Skip when output-env-credentials is false: the credentials were never written to env,
-      // so the default credential provider chain would resolve to ambient runner credentials
-      // (e.g. an EC2 instance profile) and the access-key-id check would spuriously fail.
-      // Skip when using a profile: validation runs after the profile file is written below.
-      if ((!process.env.GITHUB_ACTIONS || AccessKeyId) && !awsProfile && outputEnvCredentials) {
-        await withRetry(
-          () =>
-            credentialsClient.validateCredentials(
-              roleCredentials.Credentials?.AccessKeyId,
-              roleChaining,
-              expectedAccountIds,
-            ),
-          'validateCredentials',
-        );
-      }
+      // Validate the assumed-role credentials and resolve their identity.
+      const identity = await withRetry(
+        () => credentialsClient.validateCredentials(toCredentialIdentity(roleCredentials.Credentials)),
+        'validateCredentials',
+      );
+      // Enforce the allowed-account-ids guardrail against the assumed (final) account.
+      validateAccountId(expectedAccountIds, identity.Account);
       if (outputEnvCredentials) {
-        await withRetry(() => exportAccountId(credentialsClient, maskAccountId), 'exportAccountId');
+        exportAccountId(identity, maskAccountId);
       }
 
       // Write profile files if profile mode is enabled
@@ -279,18 +283,8 @@ export async function run() {
         }
         // If user provided IAM User Credentials and then we assumed a role, overwrite the profile file to add
         // the session token. (this only overwrites the profile within a single run of the action).
-        // We then validate the credentials to make sure they work.
         if (AccessKeyId || !process.env.GITHUB_ACTIONS) {
           writeProfileFiles(awsProfile, roleCredentials.Credentials, region, true);
-          await withRetry(
-            () =>
-              credentialsClient.validateCredentials(
-                roleCredentials.Credentials?.AccessKeyId,
-                roleChaining,
-                expectedAccountIds,
-              ),
-            'validateCredentials',
-          );
         } else {
           writeProfileFiles(awsProfile, roleCredentials.Credentials, region, overwriteAwsProfile);
         }

test/index.test.ts

@@ -618,6 +618,9 @@ describe('Configure AWS Credentials', {}, () => {
     });
     it("doesn't export credentials as environment variables if told not to", {}, async () => {
       mockedSTSClient.on(AssumeRoleWithWebIdentityCommand).resolvesOnce(mocks.outputs.STS_CREDENTIALS);
+      // Credentials are validated (and their account resolved) even when not exported to the
+      // environment, so GetCallerIdentity is now called on the explicit assumed-role credentials.
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
       vi.mocked(core.getInput).mockImplementation(mocks.getInput(mocks.NO_ENV_CREDS_INPUTS));
       vi.mocked(core.getIDToken).mockResolvedValue('testoidctoken');
       process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN = 'fake-token';
@@ -628,6 +631,7 @@ describe('Configure AWS Credentials', {}, () => {
     });
     it('can export creds as step outputs without exporting as env variables', {}, async () => {
       mockedSTSClient.on(AssumeRoleWithWebIdentityCommand).resolvesOnce(mocks.outputs.STS_CREDENTIALS);
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
       vi.mocked(core.getInput).mockImplementation(mocks.getInput(mocks.STEP_BUT_NO_ENV_INPUTS));
       vi.mocked(core.getIDToken).mockResolvedValue('testoidctoken');
       process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN = 'fake-token';
@@ -897,6 +901,65 @@ describe('Configure AWS Credentials', {}, () => {
       expect(core.info).toHaveBeenCalledWith('Authenticated as assumedRoleId AROAFAKEASSUMEDROLEID');
     });
 
+    it('fails with OIDC when account ID does not match allowed list', async () => {
+      // Regression test for the allowed-account-ids bypass: in a real runner (GITHUB_ACTIONS=true)
+      // authenticating via OIDC, the account-ID guardrail was previously never enforced.
+      vi.mocked(core.getInput).mockImplementation(
+        mocks.getInput({
+          ...mocks.GH_OIDC_INPUTS,
+          'allowed-account-ids': '999999999999',
+        }),
+      );
+      vi.mocked(core.getIDToken).mockResolvedValue('testoidctoken');
+      mockedSTSClient.on(AssumeRoleWithWebIdentityCommand).resolves(mocks.outputs.STS_CREDENTIALS);
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
+      process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN = 'fake-token';
+
+      await run();
+      expect(core.setFailed).toHaveBeenCalledWith(
+        'The account ID of the provided credentials (111111111111) does not match any of the expected account IDs: 999999999999',
+      );
+    });
+
+    it('fails with OIDC and output-env-credentials false when account ID does not match', async () => {
+      // The guardrail must hold even when credentials are never written to the environment.
+      vi.mocked(core.getInput).mockImplementation(
+        mocks.getInput({
+          ...mocks.NO_ENV_CREDS_INPUTS,
+          'allowed-account-ids': '999999999999',
+        }),
+      );
+      vi.mocked(core.getIDToken).mockResolvedValue('testoidctoken');
+      mockedSTSClient.on(AssumeRoleWithWebIdentityCommand).resolves(mocks.outputs.STS_CREDENTIALS);
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
+      process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN = 'fake-token';
+
+      await run();
+      expect(core.setFailed).toHaveBeenCalledWith(
+        'The account ID of the provided credentials (111111111111) does not match any of the expected account IDs: 999999999999',
+      );
+    });
+
+    it('fails with assume role when assumed account ID does not match allowed list', async () => {
+      vi.mocked(core.getInput).mockImplementation(
+        mocks.getInput({
+          ...mocks.IAM_ASSUMEROLE_INPUTS,
+          'allowed-account-ids': '999999999999',
+        }),
+      );
+      mockedSTSClient.on(AssumeRoleCommand).resolves(mocks.outputs.STS_CREDENTIALS);
+      mockedSTSClient.on(GetCallerIdentityCommand).resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
+      // biome-ignore lint/suspicious/noExplicitAny: any required to mock private method
+      vi.spyOn(CredentialsClient.prototype as any, 'loadCredentials')
+        .mockResolvedValueOnce({ accessKeyId: 'MYAWSACCESSKEYID' })
+        .mockResolvedValueOnce({ accessKeyId: 'STSAWSACCESSKEYID' });
+
+      await run();
+      expect(core.setFailed).toHaveBeenCalledWith(
+        'The account ID of the provided credentials (111111111111) does not match any of the expected account IDs: 999999999999',
+      );
+    });
+
     it('handles GetCallerIdentity API failure gracefully', async () => {
       vi.mocked(core.getInput).mockImplementation(
         mocks.getInput({
@@ -911,7 +974,11 @@ describe('Configure AWS Credentials', {}, () => {
       });
 
       await run();
-      expect(core.setFailed).toHaveBeenCalledWith('Could not validate account ID of credentials: API Error');
+      // The account allow-list now reuses the single liveness GetCallerIdentity call, so an STS
+      // failure surfaces as a credential-loading failure rather than a dedicated account-check error.
+      expect(core.setFailed).toHaveBeenCalledWith(
+        'Credentials could not be loaded, please check your action inputs: API Error',
+      );
     });
 
     it('ignores validation when allowed-account-ids is empty', async () => {
@@ -1373,7 +1440,7 @@ describe('Configure AWS Credentials', {}, () => {
   });
 
   describe('Retry Behavior', {}, () => {
-    it('retries exportAccountId on transient GetCallerIdentity failure', async () => {
+    it('retries validateCredentials on transient GetCallerIdentity failure', async () => {
       vi.mocked(core.getInput).mockImplementation(mocks.getInput(mocks.IAM_USER_INPUTS));
       // biome-ignore lint/suspicious/noExplicitAny: any required to mock private method
       vi.spyOn(CredentialsClient.prototype as any, 'loadCredentials').mockResolvedValue({
@@ -1384,7 +1451,9 @@ describe('Configure AWS Credentials', {}, () => {
         .rejectsOnce(new Error('throttled'))
         .resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
       await run();
-      expect(core.info).toHaveBeenCalledWith(expect.stringContaining('Retry exportAccountId'));
+      // The single liveness GetCallerIdentity call lives in validateCredentials, so transient STS
+      // failures are retried under that label (the account ID is then resolved without a second call).
+      expect(core.info).toHaveBeenCalledWith(expect.stringContaining('Retry validateCredentials'));
       expect(core.setFailed).not.toHaveBeenCalled();
     });
 
@@ -1414,7 +1483,7 @@ describe('Configure AWS Credentials', {}, () => {
       expect(core.info).not.toHaveBeenCalledWith(expect.stringContaining('Retry'));
     });
 
-    it('retries exportAccountId after role assumption (issue #1681)', async () => {
+    it('retries the post-assume identity check on a transient invalid-token error (issue #1681)', async () => {
       vi.mocked(core.getInput).mockImplementation(mocks.getInput(mocks.GH_OIDC_INPUTS));
       vi.mocked(core.getIDToken).mockResolvedValue('testoidctoken');
       mockedSTSClient.on(AssumeRoleWithWebIdentityCommand).resolves(mocks.outputs.STS_CREDENTIALS);
@@ -1424,7 +1493,9 @@ describe('Configure AWS Credentials', {}, () => {
         .resolves({ ...mocks.outputs.GET_CALLER_IDENTITY });
       process.env.ACTIONS_ID_TOKEN_REQUEST_TOKEN = 'fake-token';
       await run();
-      expect(core.info).toHaveBeenCalledWith(expect.stringContaining('Retry exportAccountId'));
+      // Freshly-assumed credentials can be briefly rejected by STS (eventual consistency). The
+      // liveness GetCallerIdentity now runs inside validateCredentials, so the retry happens there.
+      expect(core.info).toHaveBeenCalledWith(expect.stringContaining('Retry validateCredentials'));
       expect(core.info).toHaveBeenCalledWith(
         expect.stringContaining('The security token included in the request is invalid'),
       );