Revealing the Inner Structure of AWS Session Tokens

A recent study by Tal Be'ery has successfully reverse-engineered AWS Session Tokens, previously considered opaque. This research reveals the internal structure of these tokens, which are crucial for AWS's security model, allowing for temporary, limited-privilege credentials. The study highlights the importance of understanding AWS's authentication and authorization protocols, especially as attackers often exploit these systems to gain unauthorized access. The AWS Security Token Service (STS) provides short-term credentials that include an ID, Secret, and a Session Token, which is encrypted and contains a validity period to mitigate risks associated with credential theft.

The research process involved decoding the Session Token, revealing a structured format that can be analyzed and manipulated. Be'ery's team developed two open-source tools: the AWS Token Decoder, which parses the token into fields, and the STS-token-decoder, which allows for programmatic analysis and synthesis of tokens. These tools enable users to efficiently analyze multiple tokens and modify them as needed, enhancing the understanding of AWS's security mechanisms.

The findings emphasize the need for defenders to comprehend the intricacies of AWS's authentication systems to better protect against potential attacks. The research not only sheds light on the cryptographic and authentication protocols used by AWS but also provides valuable resources for security professionals to analyze and improve their defenses against credential-based attacks.