CVE-2025-59420

unknown

Published 2025-09-22 · Modified 2026-02-04

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CVSS v3

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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS v4 NEW

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not yet in upstream

VIR risk

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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.

Predictions

Exploit likelihood

30%

Patch ETA

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Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

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OS impact

Debian Fixed 5 releases

Version	Status	Fixed in
trixie	Fixed	`1.6.0-1+deb13u1`
sid	Fixed	`1.6.4-1`
forky	Fixed	`1.6.4-1`
bullseye	Fixed	`0.15.4-1+deb11u1`
bookworm	Fixed	`1.2.0-1+deb12u1`

Package impact

Ecosystem	Package	Vulnerable	Fixed
PyPI	authlib	`<1.6.4`	`1.6.4`

References

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.