CVE-2025-61920: high-severity vulnerability in authlib
Authlib is vulnerable to Denial of Service via Oversized JOSE Segments
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.5epss 0.6%
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
authlib · authlibRelated CVEs — authlib
In the same product, most dangerous first.
CVE-2026-27962CRITICALAuthlib JWS JWK Header Injection: Signature Verification BypassEPSS 0.6%CVE-2026-28802HIGHAuthlib: Setting `alg: none` and a blank signature appears to bypass signature verificationEPSS 0.5%CVE-2025-62706MEDIUMAuthlib : JWE zip=DEF decompression bomb enables DoSEPSS 0.5%CVE-2026-114620MEDIUMAuthlib: Unvalidated request_uri fetch in JWT-secured authorization request (JAR) leading to SSRFEPSS 0.4%CVE-2026-114618MEDIUMAuthlib: Default JWT bearer grant accepts assertions for the wrong audienceEPSS 0.4%CVE-2026-114616HIGHAuthlib accepts an empty HMAC key, allowing JWS/JWT signature forgery (HS256/HS384/HS512)EPSS 0.3%