CVE-2026-28498 — Security Box Score

CVE · referencelatest edition

Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-28498HIGH

Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   H   P   N   N   N   H   N    8.2   .0023   13.6     —

AFFECTED
  Product  Versions   Fixed
  authlib  < 1.6.9 –  —

TIMELINE
  Feb 27  Reserved by GitHub_M
  Mar 16  Published (CNA: GitHub_M)
  Aug 17  EXPLOIT PUBLISHED — CVE-2026-28498 (authlib). Public exploit reference added.

CWE-354, CWE-573 · CNA: GitHub_M · CVSS v4.0 · 12 references · NVD 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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
February 27, 2026	Reserved	Reserved by GitHub_M
March 16, 2026	Published	Published (CNA: GitHub_M)
August 17, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-28498 (authlib). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
authlib	authlib	—	< 1.6.9	—

Weaknesses

CWE-354 · CWE-573

References (12)

https://access.redhat.com/errata/RHSA-2026:6309 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:6497 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:6567 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:6568 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:6720 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/errata/RHSA-2026:6912 [vendor-advisory, x_refsource_REDHAT]
https://access.redhat.com/security/cve/CVE-2026-28498 [vdb-entry, x_refsource_REDHAT]
https://bugzilla.redhat.com/show_bug.cgi?id=2448182 [issue-tracking, x_refsource_REDHAT]
https://github.com/authlib/authlib/commit/b9bb2b25bf8b7e01512d847a95c1749646eaa72b [x_refsource_MISC]
https://github.com/authlib/authlib/releases/tag/v1.6.9 [x_refsource_MISC]
https://github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6j [x_refsource_CONFIRM]
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28498.json [x_sadp-csaf-vex]

Authoritative record: CVE-2026-28498 at cve.org

Vendors: authlib

Weaknesses: CWE-354 · CWE-573

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-28498 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.