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Article by Nick Frichette.

Enumerate AWS Account ID from a Public S3 Bucket

Note

The documentation and GitHub repository refer to this tool as s3-account-search, however when it is installed using pip, it is named s3-account-finder. Because of this, all the examples below will use the s3-account-finder name.

By leveraging the s3:ResourceAccount policy condition, we can identify the AWS account ID associated with a public S3 bucket. This is possible because it supports wildcards (*). With this, we can sequentially enumerate the account ID.

To test this, you can use Grayhat Warfare's list of public S3 buckets.

You will need a role with s3:getObject and s3:ListBucket permissions, and you can specify the target bucket as the resource for your policy. Alternatively you can set a resource of '*' to quickly test multiple buckets.

Installation

The tool can be installed with the following command:

python3 -m pip install s3-account-search

Setup

To use the tool, there is some setup on your end. You will need your own AWS account with a role you can assume with the s3:GetObject or s3:ListBucket permissions. s3-account-finder will assume this role so make sure the credentials you're using can do this.

Usage

s3-account-finder arn:aws:iam::123456789123:role/s3-searcher <bucket name>
Starting search (this can take a while)
found: 1
found: 12
*** snip ***
found: 123456789123

Operational Security Tip

The majority of this activity would only be logged to the calling account (the account you are running the tool with), however S3 data events and server access logging can be used to see the API activity. That being said, there is no immediate way to counter or prevent you from doing this. Additionally these requests could be spaced out over an extended period of time, further making it difficult to identify.

Tip

Pair this with Unauthenticated Enumeration of IAM Users and Roles!