Authlib JWS JWK Header Injection: Signature Verification Bypass
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Security bypass
- Confidentiality · integrity · availability
- High · High · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-347.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- Yes
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| authlib | authlib | before 1.6.9 | 1.6.9 | Patch available | CNA |
| — | authlib (PyPI) | before 1.6.9 | 1.6.9 | Patch available | GHSA-wvwj-cvrp-7pv5 |
- authlib Vendorauthlib Affected before 1.6.9 Fixed in 1.6.9 Patch available CNA
- authlib (PyPI) Vendor— Affected before 1.6.9 Fixed in 1.6.9 Patch available GHSA-wvwj-cvrp-7pv5
Remediation
- Fix · CNA authlib (authlib) Fixed in 1.6.9
- Fix · GHSA-wvwj-cvrp-7pv5 authlib (PyPI) Fixed in 1.6.9 Advisory →
Red Hat 5 advisories
- RHSA-2026:48085 Released 2026-07-29 · Red Hat rating ImportantRed Hat Quay 3.18.0
- Red Hat Quay 3.18 registry.redhat.io/quay/quay-rhel9
- RHSA-2026:24853 Released 2026-06-09 · Red Hat rating ImportantRed Hat Quay 3.15.5
- Red Hat Quay 3.15 registry.redhat.io/quay/quay-rhel8
- RHSA-2026:19375 Released 2026-05-19 · Red Hat rating ImportantRed Hat Quay 3.16.4
- Red Hat Quay 3.16 registry.redhat.io/quay/quay-rhel9
Show 2 more Red Hat advisories
- RHSA-2026:7314 Released 2026-04-09 · Red Hat rating ImportantRed Hat Quay 3.14.7
- Red Hat Quay 3.14 registry.redhat.io/quay/quay-rhel8
- RHSA-2026:5665 Released 2026-03-24 · Red Hat rating ImportantRed Hat Quay 3.10.19
- Red Hat Quay 3.10 registry.redhat.io/quay/quay-rhel8
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Quay 3.10 | Fixed | RHSA-2026:5665 |
| Red Hat Quay 3.14 | Fixed | RHSA-2026:7314 |
| Red Hat Quay 3.15 | Fixed | RHSA-2026:24853 |
| Red Hat Quay 3.16 | Fixed | RHSA-2026:19375 |
| Red Hat Quay 3.18 | Fixed | RHSA-2026:48085 |
Not affected: 9 products
- Lightspeed Core
- Red Hat Ansible Automation Platform 2
- Red Hat OpenShift AI (RHOAI)
- Red Hat Quay 3.10
- Red Hat Quay 3.14
- Red Hat Quay 3.15
- Red Hat Quay 3.16
- Red Hat Quay 3.18
- Red Hat Satellite 6
Timeline
- 2026-10-02 Threatist record created from CVE-2026-27962
- 2026-10-03 Alias added: GHSA-wvwj-cvrp-7pv5
References
Other 12
- https://github.com/authlib/authlib/releases/tag/v1.6.9
- https://access.redhat.com/errata/RHSA-2026:19375
- https://access.redhat.com/errata/RHSA-2026:24853
- https://access.redhat.com/errata/RHSA-2026:48085
- https://access.redhat.com/errata/RHSA-2026:5665
- https://access.redhat.com/errata/RHSA-2026:7314
- https://access.redhat.com/security/cve/CVE-2026-27962
- https://bugzilla.redhat.com/show_bug.cgi?id=2448164
- https://github.com/authlib/authlib
- https://github.com/pypa/advisory-database/tree/main/vulns/authlib/PYSEC-2026-287.yaml
- https://pypi.org/project/authlib
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27962.json
More Authlib vulnerabilities
- TI-2026-79518 Authlib fix bypass lets attackers forge HS256 tokens with PEM keys CVSS 3.1CRITICAL 9.1
- TI-2025-36973 Authlib: JWS/JWT accepts unknown crit headers (RFC violation → possible authz bypass) CVSS 3.1HIGH 7.5
- TI-2024-25068 lepture Authlib before 1.3.1 has algorithm confusion with asymmetric public keys. CVSS 3.1HIGH 7.5
- TI-2025-41738 Authlib: 1-click Account Takeover CVSS 3.1HIGH 8.8
- TI-2026-22761 Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding CVSS 4.0HIGH 8.2
- TI-2026-22754 Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle CVSS 4.0HIGH 8.3
Sources
- CVE-2026-27962 · CVE Program
- CVE-2026-27962 · NVD
- FIRST EPSS
- GHSA-wvwj-cvrp-7pv5 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-27962 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences