{"cve":"CVE-2025-61920","nvd":{"published":"2025-10-10T20:15:37.893","modified":"2026-10-19T16:10:00.260","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-20","CWE-400","CWE-770"],"references":["https://github.com/authlib/authlib/commit/867e3f87b072347a1ae9cf6983cc8bbf88447e5e","https://github.com/authlib/authlib/security/advisories/GHSA-pq5p-34cr-23v9","https://lists.debian.org/debian-lts-announce/2025/10/msg00032.html"],"products":["authlib:authlib"],"source":"nvd","synced_at":"2026-10-19T22:11:26.888974865+00:00"},"epss":{"cve":"CVE-2025-61920","score":0.00638,"percentile":0.50296,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-pq5p-34cr-23v9","url":"https://osv.dev/vulnerability/GHSA-pq5p-34cr-23v9","summary":"Authlib is vulnerable to Denial of Service via Oversized JOSE Segments","modified":"2026-09-10T03:50:30.223430893Z","packages":[{"ecosystem":"PyPI","name":"authlib","purl":"pkg:pypi/authlib","ranges":["<1.6.5"],"fixed":["1.6.5"]}]},{"id":"PYSEC-2026-1203","url":"https://osv.dev/vulnerability/PYSEC-2026-1203","summary":"Authlib is vulnerable to Denial of Service via Oversized JOSE Segments","modified":"2026-07-07T17:46:32.726793400Z","packages":[{"ecosystem":"PyPI","name":"authlib","purl":"pkg:pypi/authlib","ranges":["<1.6.5"],"fixed":["1.6.5"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}