{"cve":"CVE-2026-28498","nvd":{"published":"2026-03-16T18:16:07.717","modified":"2026-09-10T13:18:01.797","status":"Modified","description":"Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N","score":8.2},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-354","CWE-573","CWE-325"],"references":["https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b","https://github.com/authlib/authlib/releases/tag/v1.6.9","https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j","https://access.redhat.com/errata/RHSA-2026:6309","https://access.redhat.com/errata/RHSA-2026:6497"],"products":["authlib:authlib"],"source":"nvd","synced_at":"2026-10-19T22:26:19.218427112+00:00"},"epss":{"cve":"CVE-2026-28498","score":0.00235,"percentile":0.14437,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-m344-f55w-2m6j","url":"https://osv.dev/vulnerability/GHSA-m344-f55w-2m6j","summary":"Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding","modified":"2026-07-13T07:26:18.508336668Z","packages":[{"ecosystem":"PyPI","name":"authlib","purl":"pkg:pypi/authlib","ranges":["<1.6.9"],"fixed":["1.6.9"]}]},{"id":"PYSEC-2026-2117","url":"https://osv.dev/vulnerability/PYSEC-2026-2117","summary":"","modified":"2026-07-13T07:15:14.229577118Z","packages":[{"ecosystem":"PyPI","name":"authlib","purl":"pkg:pypi/authlib","ranges":["<1.6.9"],"fixed":["1.6.9"]}]}],"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."]}