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.
Advisories
Source ID Title
Github GHSA Github GHSA GHSA-pq5p-34cr-23v9 Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Sat, 11 Oct 2025 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Fri, 10 Oct 2025 21:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 10 Oct 2025 19:30:00 +0000

Type Values Removed Values Added
Description 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.
Title Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
Weaknesses CWE-20
CWE-400
CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2025-10-10T20:47:08.736Z

Reserved: 2025-10-03T22:21:59.615Z

Link: CVE-2025-61920

cve-icon Vulnrichment

Updated: 2025-10-10T20:47:02.479Z

cve-icon NVD

Status : Received

Published: 2025-10-10T20:15:37.893

Modified: 2025-10-10T20:15:37.893

Link: CVE-2025-61920

cve-icon Redhat

Severity : Important

Publid Date: 2025-10-10T19:25:07Z

Links: CVE-2025-61920 - Bugzilla

cve-icon OpenCVE Enrichment

No data.