AWS Secrets Manager call from Lambda returning null/none

Question

I am using an AWS Lambda function to call AWS Secrets Manager for retrieving secret values but it just returns the value None/Null.

Here is my code:

# Secrets Manager
import boto3
import base64
from botocore.exceptions import ClientError


def lambda_handler(event, context):
    # Secrets Manager
    def get_secret():

        secret_name = "arn:aws:secretsmanager:region:accountid:secret:full-secret-name"
        region_name = "region"

        # Create a Secrets Manager client
        session = boto3.session.Session()
        client = session.client(
            service_name='secretsmanager',
            region_name=region_name
        )

        # Only handle the specific exceptions for the 'GetSecretValue' API.
        # See https://docs.aws.amazon.com/secretsmanager/latest/apireference/API_GetSecretValue.html
        # We rethrow the exception by default.

        try:
            get_secret_value_response = client.get_secret_value(
                SecretId=secret_name
            )
        except ClientError as e:
            if e.response['Error']['Code'] == 'DecryptionFailureException':
                # Secrets Manager can't decrypt the protected secret text using the provided KMS key.
                # Deal with the exception here, and/or rethrow at your discretion.
                raise e
            elif e.response['Error']['Code'] == 'InternalServiceErrorException':
                # An error occurred on the server side.
                # Deal with the exception here, and/or rethrow at your discretion.
                raise e
            elif e.response['Error']['Code'] == 'InvalidParameterException':
                # You provided an invalid value for a parameter.
                # Deal with the exception here, and/or rethrow at your discretion.
                raise e
            elif e.response['Error']['Code'] == 'InvalidRequestException':
                # You provided a parameter value that is not valid for the current state of the resource.
                # Deal with the exception here, and/or rethrow at your discretion.
                raise e
            elif e.response['Error']['Code'] == 'ResourceNotFoundException':
                # We can't find the resource that you asked for.
                # Deal with the exception here, and/or rethrow at your discretion.
                raise e
        else:
            # Decrypts secret using the associated KMS CMK.
            # Depending on whether the secret is a string or binary, one of these fields will be populated.
            if 'SecretString' in get_secret_value_response:
                secret = get_secret_value_response['SecretString']
            else:
                decoded_binary_secret = base64.b64decode(get_secret_value_response['SecretBinary'])

    secretValue = get_secret()
    print(secretValue)
    return secretValue

In the return, I get null and in the print I get None. Not really sure what I am doing wrong here but it does not error out nor get my value.

The Secret is encrypted but the Lambda IAM Role has use permissions of the KMS key and the KMS key has granted the IAM Role usage as well.

I have also tried setting secret_name to just the Secrets Name like so:

secret_name = "full-secret-name-no-arn"

Regards

Answer 1

Your get_secret() doesn't have return statement

Answer 2

In addition to the above changes, ensure that your Lambda Execution role has the appropriate privileges for accessing secret manager and KMS services. Here is the sample IAM policy to be attached to the execution role. When applied, the below policy will allow Lambda to retrieve the secret without returning 'None.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "logs:CreateLogGroup",
            "Resource": "arn:aws:logs:us-west-2:<ACCOUNT_ID>:*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": [
                "arn:aws:logs:us-west-2:<ACCOUNT_ID>:log-group:/aws/lambda/sampletest*:*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "secretsmanager:GetSecretValue",
                "secretsmanager:DescribeSecret",
                "secretsmanager:ListSecretVersionIds",
                "secretsmanager:PutSecretValue",
                "secretsmanager:UpdateSecret",
                "secretsmanager:TagResource",
                "secretsmanager:UntagResource"
            ],
            "Resource": [
                "arn:aws:secretsmanager:us-west-2:<ACCOUNT_ID>:secret:<SECRET_NAME>"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "kms:Decrypt"
            ],
            "Resource": "arn:aws:kms:us-west-2:<ACCOUNT_ID>:key/<KMS_ID>"
        }
    ]
}

Answer 3

The problem is tricky ... as AWS does not give you any valuable log INFO about the lack of permissions to access the secrets manager service. You need to work on the IAM role of the process you are running and add the proper permissions for Secrets Manager access and it will go through no problem !!!

It is a really frustation AWS just returns 'None' without giving you any error message :(