CVE-2025-59420

Summary

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.

Affected Software

VendorProductVersion RangeStatus
authlibauthlib< 1.6.4affected

Weaknesses

  • CWE-345: CWE-345: Insufficient Verification of Data Authenticity
  • CWE-863: CWE-863: Incorrect Authorization

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: poc
    • Automatable: yes
    • Technical Impact: partial

CVE Program Container

Additional References

References