Is CVE-2026-28498 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-28498 being exploited in the wild.

How severe is CVE-2026-28498?

High severity, with a CVSS score of 7.5, published 16 March 2026.

Which products and versions are affected?

authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.9.

Is there a fix for CVE-2026-28498?

Yes. authlib (PyPI): upgrade to 1.6.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-28498 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-28498?

Check whether you run authlib (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-28498: Authlib fail-open cryptographic verification in OIDC hash binding

CVE-2026-28498 · Severity: high · CVSS 7.5 · Published 2026-03-16

Authlib is a popular Python library used by developers to build secure login systems using standards like OAuth and OpenID Connect. A flaw in the library's security checks allows an attacker to bypass mandatory integrity protections by using a specially crafted login token. This could allow an attacker to substitute legitimate security codes or access tokens with malicious ones, potentially leading to unauthorized access or account takeover in applications that rely on this library.

Technologies: authlib (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-28498 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-28498 being exploited in the wild.
How severe is CVE-2026-28498?: High severity, with a CVSS score of 7.5, published 16 March 2026.
Which products and versions are affected?: authlib (PyPI) ECOSYSTEM:introduced=0,fixed=1.6.9.
Is there a fix for CVE-2026-28498?: Yes. authlib (PyPI): upgrade to 1.6.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-28498 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-28498?: Check whether you run authlib (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

authlib (PyPI): upgrade to 1.6.9 or later
```
pip install "authlib>=1.6.9"
```

Technical details

A vulnerability exists in Authlib's internal hash verification logic (_verify_hash) within authlib/oidc/core/claims.py. When validating the at_hash (Access Token Hash) or c_hash (Authorization Code Hash) claims, the library calls create_half_hash. If an attacker provides a forged ID Token with an unsupported or unknown 'alg' header parameter, create_half_hash returns None. The _verify_hash function incorrectly interprets this None value as a successful validation and returns True instead of failing. This fail-open state allows an attacker to perform token substitution attacks in Hybrid or Implicit OIDC flows, bypassing the cryptographic binding between the ID Token and the Access Token or Authorization Code. The issue is fixed in version 1.6.9 by ensuring the function returns False when the hash cannot be computed.

Affected products

authlib Authlib <= 1.6.8
Red Hat Red Hat Ansible Automation Platform 2.6
Red Hat Red Hat Quay 3.12
Red Hat Red Hat Quay 3.15
Red Hat Red Hat Quay 3.16
Red Hat Red Hat Satellite 6

Identifiers

CVE-2026-28498
GHSA-m344-f55w-2m6j
PYSEC-2026-2117

Timeline

2026-03-02: patched: Version 1.6.9 released
2026-03-15: advisory: GitHub Security Advisory published
2026-03-16: disclosed: CVE published to NVD

References

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