Improper Input Validation

Summary

Authlib is a Python library that builds OAuth and OpenID Connect servers. Prior to version 1.6.5, Authlibs JOSE implementation accepts unbounded JWS/JWT header and signature segments. A remote attacker can craft a token whose 'base64urlencoded' header or signature spans hundreds of megabytes. During verification, Authlib decodes and parses the full input before it is rejected, driving CPU and memory consumption to hostile levels and enabling Denial-of-Service (DoS). Some temporary workarounds are available. Enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.