Resource exhaustion in Authlib
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.
Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)
EPSS: 0.006 (45.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
Affected products
- Authlib — versions < 1.6.5
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Mitigation, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2025-61920?
- CVE-2025-61920 is a high-severity vulnerability in Authlib, classified under Improper Input Validation. CVSS score: 7.5/10. Published 2025-10-10.
- How severe is CVE-2025-61920?
- High severity. CVSS v3 base score is 7.5 out of 10.