CVE-2025-68481

FastAPI Users allows users to quickly add a registration and authentication system to their FastAPI project. Prior to version 15.0.2, the OAuth login state tokens are completely stateless and carry no per-request entropy or any data that could link them to the session that initiated the OAuth flow. generate_state_token() is always called with an empty state_data dict, so the resulting JWT only contains the fixed audience claim plus an expiration timestamp. On callback, the library merely checks that the JWT verifies under state_secret and is unexpired; there is no attempt to match the state value to the browser that initiated the OAuth request, no correlation cookie, and no server-side cache. Any attacker can hit /authorize, capture the server-generated state, finish the upstream OAuth flow with their own provider account, and then trick a victim into loading .../callback?code=<attacker_code>&state=<attacker_state>. Because the state JWT is valid for any client for ~1 hour, the victim’s browser will complete the flow. This leads to login CSRF. Depending on the app’s logic, the login CSRF can lead to an account takeover of the victim account or to the victim user getting logged in to the attackers account. Version 15.0.2 contains a patch for the issue.

Weakness

The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.

Potential Mitigations

• Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) to enforce the roles at the appropriate boundaries.
• Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
• For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
• One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/1.html
• https://cwe.mitre.org/data/definitions/104.html
• https://cwe.mitre.org/data/definitions/127.html
• https://cwe.mitre.org/data/definitions/13.html
• https://cwe.mitre.org/data/definitions/17.html
• https://cwe.mitre.org/data/definitions/39.html
• https://cwe.mitre.org/data/definitions/402.html
• https://cwe.mitre.org/data/definitions/45.html
• https://cwe.mitre.org/data/definitions/5.html
• https://cwe.mitre.org/data/definitions/51.html
• https://cwe.mitre.org/data/definitions/59.html
• https://cwe.mitre.org/data/definitions/60.html
• https://cwe.mitre.org/data/definitions/647.html
• https://cwe.mitre.org/data/definitions/668.html
• https://cwe.mitre.org/data/definitions/76.html
• https://cwe.mitre.org/data/definitions/77.html
• https://cwe.mitre.org/data/definitions/87.html

References

• https://github.com/fastapi-users/fastapi-users/blob/bcee8c9b884de31decb5d799aead3974a0b5b158/fastapi_users/router/oauth.py#L111
• https://github.com/fastapi-users/fastapi-users/blob/bcee8c9b884de31decb5d799aead3974a0b5b158/fastapi_users/router/oauth.py#L57
• https://github.com/fastapi-users/fastapi-users/commit/7cf413cd766b9cb0ab323ce424ddab2c0d235932
• https://github.com/fastapi-users/fastapi-users/security/advisories/GHSA-5j53-63w8-8625