authlib: Improper Validation of Integrity Check Value
CVE-2026-28498 is a high-severity improper validation of integrity check value vulnerability in authlib, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected authlib versions: < 1.6.9. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.26% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of authlib you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Authlib | authlib | < 1.6.9 | Not stated |
| Red Hat | Red Hat Ansible Automation Platform 2.6 | Not specified in the record | Not stated |
| Red Hat | Red Hat Quay 3.10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Quay 3.12 | Not specified in the record | Not stated |
| Red Hat | Red Hat Quay 3.15 | Not specified in the record | Not stated |
| Red Hat | Red Hat Quay 3.16 | Not specified in the record | Not stated |
| Red Hat | Lightspeed Core | Not specified in the record | Not stated |
| Red Hat | Red Hat Ansible Automation Platform 2 | Not specified in the record | Not stated |
| Red Hat | Red Hat OpenShift AI (RHOAI) | Not specified in the record | Not stated |
| Red Hat | Red Hat Satellite 6 | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.2 | High | CNA (github.com) |
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.1 | 9.1 | Critical | CNA |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Validation of Integrity Check Value
The product does not validate or incorrectly validates the integrity check values or checksums of a message.
How developers prevent this class of flaw
- The protocol specification describes the algorithm used for calculating the checksum. It is then a matter of implementing the calculation and verifying that the calculated checksum and the received checksum match.
More Improper Validation of Integrity Check Value vulnerabilities (CWE-354)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/authlib/authlib/security/advisories/GHSA-m344-f55w-2m6jExploit, Mitigation
Patches and release notes
Other references
- access.redhat.com/errata/RHSA-2026:6309
- access.redhat.com/errata/RHSA-2026:6497
- access.redhat.com/errata/RHSA-2026:6567
- access.redhat.com/errata/RHSA-2026:6568
- access.redhat.com/errata/RHSA-2026:6720
- access.redhat.com/errata/RHSA-2026:6912
- access.redhat.com/security/cve/CVE-2026-28498
- bugzilla.redhat.com/show_bug.cgi?id=2448182
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-28498.json
Other vulnerabilities in authlib
- 8.8 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.8 Critical severity
- 9.8 Critical severity
- 9.1 Critical severity
Recent Improper Validation of Integrity Check Value vulnerabilities
- 8.2 High severity
- 8.2 High severity
- 7.5 High severity
- 7.1 High severity
- 7.5 High severity
- 9.8 Critical severity
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