Why did my Secrets Manager Lambda rotation function fail for my secret in another account?

Short description

In December 2024, Secrets Manager will change to how entities that call the PutSecretValue API action are validated. Entities that call the PutSecretValue API from a Lambda function in another account for cross-account rotation must pass a rotation token. Secrets Manager uses the rotation token to validate the identity of the entity. Lambda rotation functions then call the PutSecretValue API as part of the rotation for the secret.

If your Lambda rotation function is in the same account as the secret that it rotates, then no changes are required.

If your Lambda rotation function is in another account than the secret that it rotates, then you must update your function to pass a rotation token.

Important: It's a best practice to update your rotation function before December 2024.

Resolution

To resolve this issue, update the code in your existing rotation function to include the RotationToken parameter.

Download the Lambda function code

Complete the following steps:

1. Open the Lambda console.
2. In the navigation pane, choose Functions.
3. For Function name, select your Lambda function that rotates the secret.
4. For Download, choose one of the following options:
   Function code .zip
   AWS SAM file
   Both
5. Choose OK to save the function on your local machine.

Edit the Lambda function code

Open your code editor tool, and edit the code that you downloaded. The following are example code edits that you can make.

Code example 1: Lambda_handler

The following code shows the lambda_handler function in a Secrets Manager Lambda rotation function. Secrets Manager invokes this function multiple times during a rotation. For cross-account rotation, include the rotation_token parameter in the create_secret step.

def lambda_handler(event, context):
    """Secrets Manager Rotation Template

    This is a template for creating an AWS Secrets Manager rotation lambda

    Args:
        event (dict): Lambda dictionary of event parameters. These keys must include the following:
            - SecretId: The secret ARN or identifier
            - ClientRequestToken: The ClientRequestToken of the secret version
            - Step: The rotation step (one of createSecret, setSecret, testSecret, or finishSecret)
            - RotationToken: the rotation token to put as parameter for PutSecretValue call

        context (LambdaContext): The Lambda runtime information

    Raises:
        ResourceNotFoundException: If the secret with the specified arn and stage does not exist

        ValueError: If the secret is not properly configured for rotation

        KeyError: If the event parameters do not contain the expected keys

    """
    arn = event['SecretId']
    token = event['ClientRequestToken']
    step = event['Step']
    rotation_token = event['RotationToken']

    # Setup the client
    service_client = boto3.client('secretsmanager', endpoint_url=os.environ['SECRETS_MANAGER_ENDPOINT'])

    # Make sure the version is staged correctly
    metadata = service_client.describe_secret(SecretId=arn)
    if not metadata['RotationEnabled']:
        logger.error("Secret %s is not enabled for rotation" % arn)
        raise ValueError("Secret %s is not enabled for rotation" % arn)
    versions = metadata['VersionIdsToStages']
    if token not in versions:
        logger.error("Secret version %s has no stage for rotation of secret %s." % (token, arn))
        raise ValueError("Secret version %s has no stage for rotation of secret %s." % (token, arn))
    if "AWSCURRENT" in versions[token]:
        logger.info("Secret version %s already set as AWSCURRENT for secret %s." % (token, arn))
        return
    elif "AWSPENDING" not in versions[token]:
        logger.error("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn))
        raise ValueError("Secret version %s not set as AWSPENDING for rotation of secret %s." % (token, arn))

    if step == "createSecret":
        create_secret(service_client, arn, token, rotation_token)

    elif step == "setSecret":
        set_secret(service_client, arn, token)
    
    elif step == "testSecret":
        test_secret(service_client, arn, token)
        
    elif step == "finishSecret":
        finish_secret(service_client, arn, token)
        
    else:
        raise ValueError("Invalid step parameter")

Code example 2: create_secret

The following code example shows how to revise the create_secret function in a Secrets Manager Lambda rotation function. To allow cross-account rotation, accept the rotation_token parameter, and pass the rotation token to put_secret_value.

def create_secret(service_client, arn, token, rotation_token):
"""Create the secret

This method first checks for the existence of a secret for the passed in token. If one does not exist, it will generate a
new secret and put it with the passed in token.

Args:
service_client (client): The secrets manager service client

arn (string): The secret ARN or other identifier

token (string): The ClientRequestToken associated with the secret version

rotation_token (string): the rotation token to put as parameter for PutSecretValue call

Raises:
ResourceNotFoundException: If the secret with the specified arn and stage does not exist

"""
# Make sure the current secret exists
service_client.get_secret_value(SecretId=arn, VersionStage="AWSCURRENT")

# Now try to get the secret version, if that fails, put a new secret
try:
service_client.get_secret_value(SecretId=arn, VersionId=token, VersionStage="AWSPENDING")
logger.info("createSecret: Successfully retrieved secret for %s." % arn)
except service_client.exceptions.ResourceNotFoundException:
# Get exclude characters from environment variable
exclude_characters = os.environ['EXCLUDE_CHARACTERS'] if 'EXCLUDE_CHARACTERS' in os.environ else '/@"\'\\'
# Generate a random password
passwd = service_client.get_random_password(ExcludeCharacters=exclude_characters)

# Put the secret
service_client.put_secret_value(SecretId=arn, ClientRequestToken=token, SecretString=passwd['RandomPassword'], VersionStages=['AWSPENDING'], RotationToken=rotation_token)
logger.info("createSecret: Successfully put secret for ARN %s and version %s." % (arn, token))

Upload the updated Lambda function code

To rotate your secret, upload the updated Lambda function rotation code.

Related information

Rotation by Lambda function

My Lambda rotation function called a second function to rotate a Secrets Manager secret but it failed. Why did the second Lambda function fail?