Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS verification accepts tokens that declare unknown critical header parameters (crit), violating RFC 7515 “must‑understand” semantics. An attacker can craft a signed token with a critical header (for example, bork or cnf) that strict verifiers reject but Authlib accepts. In mixed‑language fleets, this enables split‑brain verification and can lead to policy bypass, replay, or privilege escalation. This issue has been patched in version 1.6.4.
Problem types
CWE-345: Insufficient Verification of Data Authenticity
CWE-863: Incorrect Authorization
Product status
References
lists.debian.org/debian-lts-announce/2025/10/msg00032.html
github.com/...uthlib/security/advisories/GHSA-9ggr-2464-2j32
github.com/...ommit/6b1813e4392eb7c168c276099ff7783b176479df
