Ensuring Replay-Resistant Authentication with FusionAuth

[wesley]

I’m documenting our FusionAuth system login functionality and would like to know whether FusionAuth’s authentication is replay-resistant.

To clarify, a replay attack occurs when information transmitted between two parties is captured, stored, or altered, and then “replayed” later to disrupt communication or gain unauthorized access. Replay-resistant authentication ensures that captured data cannot be reused to impersonate a user or process.

Can you confirm if FusionAuth’s authentication mechanisms are replay-resistant? Please provide relevant documentation as well.

[wesley]

FusionAuth provides replay-resistant authentication mechanisms by adhering to industry standards for the technologies it implements. The level of replay resistance depends on the authentication workflow and specific standards followed.

Key Standards:

1. OAuth 2.0:
   • FusionAuth adheres to RFC 6749, RFC 8628, and OpenID Connect Core, which include mechanisms to mitigate replay attacks (e.g., nonce and state parameters).
   • Documentation: OAuth 2.0 Authorization Code Grant Example
2. Other Standards:
   FusionAuth follows established standards for other authentication protocols, such as:
   • WebAuthn: Provides strong, cryptographic-based authentication resistant to replay attacks.
   • SAMLv2: Uses unique assertions and timestamps to prevent replay.
   • OIDC (OpenID Connect): Includes nonce and other mechanisms to mitigate replay.

Replay Resistance Considerations:

• Replay resistance is primarily ensured when these protocols are implemented as defined by their standards. FusionAuth provides the tools and configurations necessary to follow these standards.
• However, deviations from these standards or implementation flaws outside of FusionAuth’s control (e.g., improper handling of state or nonce values) could introduce vulnerabilities.