authlib: Improper Verification of Cryptographic Signature
CVE-2026-27962 is a critical-severity improper verification of cryptographic signature vulnerability in authlib, with a CVSS 3.1 base score of 9.1 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 0.61% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
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 Quay 3.10 | Not specified in the record | Not stated |
| Red Hat | Red Hat Quay 3.14 | 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 | Red Hat Quay 3.18 | 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
- HighAll data handled by the component can be read.
- 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:H/I:H/A:N. Scored by CNA (github.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.1 | Critical | CNA (github.com) |
| 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 JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attacker to forge arbitrary JWT tokens that pass signature verification. When key=None is passed to any JWS deserialization function, the library extracts and uses the cryptographic key embedded in the attacker-controlled JWT jwk header field. An attacker can sign a token with their own private key, embed the matching public key in the header, and have the server accept the forged token as cryptographically valid — bypassing authentication and authorization entirely. 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 Verification of Cryptographic Signature
The product does not verify, or incorrectly verifies, the cryptographic signature for data.
More Improper Verification of Cryptographic Signature vulnerabilities (CWE-347)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5Exploit, Mitigation
Patches and release notes
Other references
- access.redhat.com/errata/RHSA-2026:19375
- access.redhat.com/errata/RHSA-2026:24853
- access.redhat.com/errata/RHSA-2026:48085
- access.redhat.com/errata/RHSA-2026:5665
- access.redhat.com/errata/RHSA-2026:7314
- access.redhat.com/security/cve/CVE-2026-27962
- bugzilla.redhat.com/show_bug.cgi?id=2448164
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27962.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
- 7.5 High severity
Recent Improper Verification of Cryptographic Signature vulnerabilities
- 8.8 High severity
- 7.5 High severity
- 9.8 Critical severity
- 9.8 Critical severity
- 7.5 High severity
- 7.2 High severity
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