High 7.5Published Sep 22, 2025

CVE-2025-59420Authlib is a Python library which builds OAuth and OpenID Connect servers.

Updated under an hour ago (2026-10-23 09:30 UTC)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for authlib

Exploited in the last 30 days

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.

CVSS: 7.5 HIGH (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness (CWE): CWE-345, CWE-863
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Not given
NVD analysis: Modified
Record last updated: Oct 19, 2026
First seen by InfoSec Signals: Oct 19, 2026

Affected products

Affected products

authlib authlib authlib:authlib	before 1.6.4	NVD

References

https://github.com/authlib/authlib/commit/6b1813e4392eb7c168c276099ff7783b176479dfpatch
https://github.com/authlib/authlib/security/advisories/GHSA-9ggr-2464-2j32exploit, vendor-advisory
https://lists.debian.org/debian-lts-announce/2025/10/msg00032.html

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.