Improper Input Validation Affecting python-authlib package, versions <0.15.5-1ubuntu0.1~esm1


Severity

Recommended
medium

Based on Ubuntu security rating.

Threat Intelligence

EPSS
0.6% (47th percentile)

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  • Snyk IDSNYK-UBUNTU2204-PYTHONAUTHLIB-13569965
  • published27 Feb 2026
  • disclosed10 Oct 2025

Introduced: 10 Oct 2025

CVE-2025-61920  (opens in a new tab)
CWE-20  (opens in a new tab)
CWE-400  (opens in a new tab)
CWE-770  (opens in a new tab)

How to fix?

Upgrade Ubuntu:22.04 python-authlib to version 0.15.5-1ubuntu0.1~esm1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream python-authlib package and not the python-authlib package as distributed by Ubuntu. See How to fix? for Ubuntu:22.04 relevant fixed versions and status.

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 Base Scores

version 3.1