Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-61920
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-10-10 20:15:37 UTC
Updated2026-10-19 16:10:00 UTC
DescriptionAuthlib 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-20 | CWE-400 | CWE-770 | CWE-20 CWE-20: Improper Input Validation | CWE-400 CWE-400: Uncontrolled Resource Consumption | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Authlib Authlib All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Authlib Authlib affected < 1.6.5 Not specified

References

ReferenceSourceLinkTags
github.com/authlib/authlib/commit/867e3f87b072347a1ae9cf6983cc8bbf88447e5e [email protected] github.com Patch
github.com/authlib/authlib/security/advisories/GHSA-pq5p-34cr-23v9 [email protected] github.com Exploit, Mitigation, Vendor Advisory
lists.debian.org/debian-lts-announce/2025/10/msg00032.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
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