← Vulnerability feed

Vulnerability record · CVE-2025-61920 · published 10 October 2025

CVE-2025-61920: Authlib improper input validation vulnerability

Authlib · Authlib

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.

7.5 CVSS 3.1 High EPSS 0.64% · top 51.5% CWE-20 · Improper input validationCWE-400 · Uncontrolled resource consumption
7.5CVSS 3.1 base score
0.64%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 1 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

Track CVE-2025-61920 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.1CVE-2026-27962Authlib improper verification of cryptographic signature vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's …EPSS 0.52%8.8CVE-2025-68158Authlib cross-site request forgery vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. In versions 1.0.0 through 1.6.5, cache-backed state/request-token storage …EPSS 0.28%8.3CVE-2026-28490Authlib observable discrepancy vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a cryptographic padding oracle vulnerability was i…EPSS 0.16%8.2CVE-2026-28498Authlib vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in th…EPSS 0.26%7.7CVE-2026-28802Authlib improper verification of cryptographic signature vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passi…EPSS 0.55%7.5CVE-2025-59420Authlib insufficient verification of data authenticity vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS verification accepts tokens that dec…EPSS 0.26%7.5CVE-2024-37568Authlib improper verification of cryptographic signature vulnerabilitylepture Authlib before 1.3.1 has algorithm confusion with asymmetric public keys. Unless an algorithm is specified in a jwt.decode call, HMAC verific…EPSS 0.38%6.5CVE-2025-62706Authlib uncontrolled resource consumption vulnerabilityAuthlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.5, Authlib’s JWE zip=DEF path performs unbounded DEFL…EPSS 0.46%

Source: NIST National Vulnerability Database (record CVE-2025-61920), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.