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CVE-2026-28498

CVE-2026-28498 · Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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 8.2 · High · EPSS 0.3% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • authlib

    Versions
    • < 1.6.9: Affected

    No fix published

  • python-authlib Debian:12

    Versions
    • 1.2.0-1
    • 1.2.0-1+deb12u1
    Affected ranges
    • ECOSYSTEM: < 1.2.0-1+deb12u2

    Update to 1.2.0-1+deb12u2

  • python-authlib Debian:13

    Versions
    • 1.6.0-1
    • 1.6.0-1+deb13u1
    • 1.6.1-1
    • 1.6.3-1
    • 1.6.4-1
    • 1.6.5-1
    • 1.6.6-1
    • 1.6.7-1
    • 1.6.8-1
    • 1.6.9-1
    • 1.7.0-1
    • 1.7.2-1
    • 1.7.2-2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-authlib Debian:14

    Versions
    • 1.6.0-1
    • 1.6.1-1
    • 1.6.3-1
    • 1.6.4-1
    • 1.6.5-1
    • 1.6.6-1
    • 1.6.7-1
    • 1.6.8-1
    Affected ranges
    • ECOSYSTEM: < 1.6.9-1

    Update to 1.6.9-1

  • authlib PyPI

    Versions
    • 0.1
    • 0.10
    • 0.11
    • 0.12
    • 0.12.1
    • 0.13
    • 0.14
    • 0.14.1
    • 0.14.2
    • 0.14.3
    • 0.15
    • 0.15.1
    • 0.15.2
    • 0.15.3
    • 0.15.4
    • 0.15.5
    • 0.15.6
    • 0.1rc0
    • 0.2
    • 0.2.1
    • 0.3
    • 0.4
    • 0.4.1
    • 0.5
    • 0.5.1
    • 0.6
    • 0.7
    • 0.8
    • 0.9
    • 1.0.0
    • 1.0.0a1
    • 1.0.0a2
    • 1.0.0b1
    • 1.0.0b2
    • 1.0.0rc1
    • 1.0.1
    • 1.1.0
    • 1.2.0
    • 1.2.1
    • 1.3.0
    • 1.3.1
    • 1.3.2
    • 1.4.0
    • 1.4.1
    • 1.5.0
    • 1.5.1
    • 1.5.2
    • 1.6.0
    • 1.6.1
    • 1.6.2
    • 1.6.3
    • 1.6.4
    • 1.6.5
    • 1.6.6
    • 1.6.7
    • 1.6.8
    Affected ranges
    • ECOSYSTEM: < 1.6.9

    Update to 1.6.9

  • python-authlib Ubuntu:Pro:22.04:LTS

    Versions
    • 0.15.4-1
    • 0.15.5-1
    • 0.15.5-1ubuntu0.1~esm1
    Affected ranges
    • ECOSYSTEM: < 0.15.5-1ubuntu0.1~esm2

    Update to 0.15.5-1ubuntu0.1~esm2

  • python-authlib Ubuntu:Pro:24.04:LTS

    Versions
    • 1.2.1-1
    • 1.3.0-1
    • 1.3.0-1ubuntu0.1~esm1
    Affected ranges
    • ECOSYSTEM: < 1.3.0-1ubuntu0.1~esm2

    Update to 1.3.0-1ubuntu0.1~esm2

  • python-authlib Ubuntu:25.10

    Versions
    • 1.5.1-1
    • 1.5.2-1
    • 1.6.0-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-authlib Ubuntu:26.10

    Versions
    • 1.6.7-1
    • 1.7.2-1
    • 1.7.2-2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-authlib Ubuntu:Pro:26.04:LTS

    Versions
    • 1.6.0-1
    • 1.6.5-1
    • 1.6.6-1
    • 1.6.7-1
    Affected ranges
    • ECOSYSTEM: < 1.6.7-1ubuntu0.1~esm1

    Update to 1.6.7-1ubuntu0.1~esm1

Original sources

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