CVE-2026-9704
Keycloak: keycloak: privilege escalation due to oversized subject_token jwt
CVSS Score
6.8
EPSS Score
0.3%
EPSS Percentile
22th
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.
| CWE | CWE-1284 |
| Vendor | red hat |
| Product | red hat build of keycloak 26.4 |
| Published | May 27, 2026 |
| Last Updated | Jun 26, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None
Affected Versions
Red Hat / Red Hat build of Keycloak 26.4
All versions affected Red Hat / Red Hat build of Keycloak 26.4
All versions affected Red Hat / Red Hat build of Keycloak 26.4
All versions affected Red Hat / Red Hat build of Keycloak 26.4.13
All versions affected Red Hat / Red Hat build of Keycloak 26.6
All versions affected Red Hat / Red Hat build of Keycloak 26.6
All versions affected Red Hat / Red Hat build of Keycloak 26.6
All versions affected Red Hat / Red Hat build of Keycloak 26.6.3
All versions affected References
access.redhat.com: https://access.redhat.com/errata/RHSA-2026:25097 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:25098 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:30049 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:30050 access.redhat.com: https://access.redhat.com/security/cve/CVE-2026-9704 bugzilla.redhat.com: https://bugzilla.redhat.com/show_bug.cgi?id=2481877
Credits
Red Hat would like to thank Filip Jovanov (PegasusMKD) for reporting this issue.