CVE-2025-61920

Publication date 10 October 2025

Last updated 27 February 2026

Ubuntu priority

Cvss 3 Severity Score

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-authlib	25.10 questing	Vulnerable
	25.04 plucky	Ignored end of life, was needs-triage
	24.04 LTS noble	Fixed 1.3.0-1ubuntu0.1~esm1
	22.04 LTS jammy	Fixed 0.15.5-1ubuntu0.1~esm1

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Severity score breakdown

Parameter	Value
Base score	7.5 · High
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	None
Availability impact	High
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

Related Ubuntu Security Notices (USN)

USN-8065-1
Authlib vulnerabilities
25 February 2026