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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.

PUBLISHED Reserved 2026-05-27 | Published 2026-05-27 | Updated 2026-05-27 | Assigner redhat




MEDIUM: 6.8CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N

Problem types

Improper Validation of Specified Quantity in Input

Product status

Default status
affected

Timeline

2026-05-27:Reported to Red Hat.
2026-05-27:Made public.

Credits

Red Hat would like to thank Filip Jovanov (PegasusMKD) for reporting this issue.

References

access.redhat.com/security/cve/CVE-2026-9704 vdb-entry

bugzilla.redhat.com/show_bug.cgi?id=2481877 (RHBZ#2481877) issue-tracking

cve.org (CVE-2026-9704)

nvd.nist.gov (CVE-2026-9704)

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