Authenticated impersonation via JWT algorithm confusion
Published Jun 25, 2026 · Updated Jun 25, 2026
JWT algorithm confusion in Red Hat build of Keycloak 26.6 before 26.6.4 allows remote authenticated users to impersonate federated users. The JWT Authorization Grant signature logic accepts alg=HS256 and uses configured Identity Provider public-key bytes as the HMAC secret instead of enforcing asymmetric verification. Exploitation requires valid client credentials, jwtAuthorizationGrantEnabled=true, useJwksUrl=false, a hardcoded public key, and no pinned assertion signature algorithm; forged assertions mint unauthorized access tokens.
Summary
What happened
JWT algorithm confusion in Red Hat build of Keycloak 26.6 before 26.6.4 allows remote authenticated users to impersonate federated users. The JWT Authorization Grant signature logic accepts alg=HS256 and uses configured Identity Provider public-key bytes as the HMAC secret instead of enforcing asymmetric verification. Exploitation requires valid client credentials, jwtAuthorizationGrantEnabled=true, useJwksUrl=false, a hardcoded public key, and no pinned assertion signature algorithm; forged assertions mint unauthorized access tokens.
The record
- CVE
- CVE-2026-11800
- Published
- Jun 25, 2026
- Updated
- Jun 25, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat build of Keycloak
- Classifications
- CWE-347, T1606
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Jun 25, 2026CVE publishedPublication date reported by the CVE source.
- Jun 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo