A flaw was found in Keycloak. An authenticated user with low privileges can exploit this vulnerability by sending an oversized subject_token JSON Web Token (JWT) to the TokenEndpoint. When the token exceeds a 4000-character limit, it is silently dropped, causing the system to fall back to client credentials. This allows the user to gain the permissions of the client's service account, leading to privilege escalation.
History

Thu, 28 May 2026 01:45:00 +0000

Type Values Removed Values Added
First Time appeared Redhat build Of Keycloak
Vendors & Products Redhat build Of Keycloak

Thu, 28 May 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Moderate


Wed, 27 May 2026 17:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 27 May 2026 14:15:00 +0000

Type Values Removed Values Added
Description A flaw was found in Keycloak. An authenticated user with low privileges can exploit this vulnerability by sending an oversized subject_token JSON Web Token (JWT) to the TokenEndpoint. When the token exceeds a 4000-character limit, it is silently dropped, causing the system to fall back to client credentials. This allows the user to gain the permissions of the client's service account, leading to privilege escalation.
Title Keycloak: keycloak: privilege escalation due to oversized subject_token jwt
First Time appeared Redhat
Redhat build Keycloak
Weaknesses CWE-1284
CPEs cpe:/a:redhat:build_keycloak:
Vendors & Products Redhat
Redhat build Keycloak
References
Metrics cvssV3_1

{'score': 6.8, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: redhat

Published: 2026-05-27T12:56:00.858Z

Updated: 2026-05-27T15:29:26.036Z

Reserved: 2026-05-27T12:39:12.284Z

Link: CVE-2026-9704

cve-icon Vulnrichment

Updated: 2026-05-27T15:29:23.173Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-05-27T14:17:40.480

Modified: 2026-05-27T14:54:20.160

Link: CVE-2026-9704

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-05-27T12:45:59Z

Links: CVE-2026-9704 - Bugzilla