Vulnerability · Published Oct 10, 2025 · Assigned by GitHub_M
CVE-2025-61920Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
High 7.5
In plain English
A high-severity improper input validation in authlib from authlib. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | python-authlib | 1.2.0-1+deb12u1 | DEBIAN-CVE-2025-61920 |
| Debian:13 | python-authlib | 1.6.0-1+deb13u1 | DEBIAN-CVE-2025-61920 |
| Debian:14 | python-authlib | 1.6.5-1 | DEBIAN-CVE-2025-61920 |
| PyPI | authlib | 1.6.5 | GHSA-pq5p-34cr-23v9 |
| PyPI | authlib | 1.6.5 | PYSEC-2026-1203 |
| Ubuntu:25.10 | python-authlib | no fix listed | UBUNTU-CVE-2025-61920 |
Affected products (as reported)
Weakness: CWE-20, CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H