CVE-2025-61920
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-10-10

Last updated on: 2025-11-03

Assigner: GitHub, Inc.

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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Meta Information
Published
2025-10-10
Last Modified
2025-11-03
Generated
2026-06-16
AI Q&A
2025-10-10
EPSS Evaluated
2026-06-15
NVD
CVE-2025-61920
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
authlib authlib to 1.6.5 (exc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-770 The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.
CWE-20 The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
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Executive Summary

This vulnerability in Authlib's JOSE implementation allows a remote attacker to craft a token with an extremely large base64url-encoded header or signature segment. When Authlib attempts to verify such a token, it decodes and parses the entire large input, causing excessive CPU and memory usage. This can lead to a denial of service condition.

Impact Analysis

The vulnerability can cause denial of service by consuming excessive CPU and memory resources during token verification. This can make the affected service unavailable or degrade its performance, impacting availability.

Mitigation Strategies

Upgrade Authlib to version 1.6.5 or later. As temporary workarounds, enforce input size limits on tokens before passing them to Authlib and implement application-level throttling to reduce the risk of denial of service attacks.

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