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CVE-2025-61920— Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

Quick assessment

Affected
authlib authlib
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Authlib是Authlib开源的一个构建 OAuth 和 OpenID Connect 服务器的终极 Python 库。 Authlib 1.6.5之前版本存在安全漏洞，该漏洞源于JOSE实现接受无限制的JWS/JWT标头和签名段，可能导致拒绝服务攻击。

CVSS 7.5 · High EPSS 0.64% · P49

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service
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I. Basic Information for CVE-2025-61920

Vulnerability Information
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Vulnerability Title
Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Authlib是Authlib开源的一个构建 OAuth 和 OpenID Connect 服务器的终极 Python 库。 Authlib 1.6.5之前版本存在安全漏洞，该漏洞源于JOSE实现接受无限制的JWS/JWT标头和签名段，可能导致拒绝服务攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
authlib authlib < 1.6.5 -

II. Public POCs for CVE-2025-61920

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9102 chars
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III. Intelligence Information for CVE-2025-61920

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Vendor Advisories for CVE-2025-61920 (1)

IV. Related Vulnerabilities

Same product: authlib
Same vendor: authlib
Same weakness: CWE-20

V. Comments for CVE-2025-61920

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