PYSEC-2026-4360

Dashboard / Vulnerabilities / PYSEC-2026-4360

PYSEC-2026-4360

Summary:

Details: Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, Authlib's RFC 9101 JWTAuthenticationRequest passes the unauthenticated, client-controlled request_uri parameter to the abstract get_request_object() hook before applying a destination or registration policy; the hook itself performs no network request, while the documentation demonstrates an unrestricted HTTP fetch. In deployments whose integrator implements that hook as an unrestricted outbound fetch, a remote attacker who knows a valid public client identifier can make the authorization server request internal, link-local, or otherwise unintended URLs and can distinguish fetch outcomes through different error responses and timing. Deployments whose custom hook already applies a secure allowlist, destination controls, and retrieval limits are not affected. The JWTAuthenticationRequest implementation in authlib/oauth2/rfc9101/authorization_server.py forwards request_uri to get_request_object() before an application-approved retrieval policy accepts the destination. This issue is fixed in version 1.9.0.

References: https://github.com/authlib/authlib/releases/tag/v1.9.0, https://github.com/authlib/authlib/commit/6563f6f7a8c2f71d2f85ee7511d72a4fbae3acc0, https://github.com/authlib/authlib/commit/891e3f10ae5989176211f8be35dcc7cd40aa92c6, https://github.com/authlib/authlib/pull/949, https://github.com/authlib/authlib/security/advisories/GHSA-x4rv-c3wx-4cr8