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High severity7.5NVD Advisory· Published Oct 10, 2025· Updated Jun 17, 2026

CVE-2025-61920

CVE-2025-61920

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.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
authlibPyPI
< 1.6.51.6.5

Affected products

13

Patches

Vulnerability mechanics

References

5

News mentions

0

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