CVE-2025-61920

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.5, Authlib’s JOSE implementation accepts unbounded JWS/JWT header and signature segments. A remote attacker can craft a token whose base64url‑encoded 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. Version 1.6.5 patches the issue. Some temporary workarounds are available. Enforce input size limits before handing tokens to Authlib and/or use application-level throttling to reduce amplification risk.

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.6% chance of exploitation in the next 30 days; higher than 50% of CVEs (scores of 2026-10-25)

CWEs

CWE-20, CWE-400, CWE-770

Published

2025-10-10

Modified

2026-10-19

Record from

the NVD, synced 2026-10-19

Affected

• authlib:authlib

Packages (OSV)

References

• https://github.com/authlib/authlib/commit/867e3f87b072347a1ae9cf6983cc8bbf88447e5e
• https://github.com/authlib/authlib/security/advisories/GHSA-pq5p-34cr-23v9
• https://lists.debian.org/debian-lts-announce/2025/10/msg00032.html

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