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Description

A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.

PUBLISHED Reserved 2026-03-23 | Published 2026-04-02 | Updated 2026-04-03 | Assigner redhat




HIGH: 7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Problem types

Excessive Platform Resource Consumption within a Loop

Product status

Default status
affected

26.2.15-1 (rpm) before *
unaffected

Default status
affected

26.2-18 (rpm) before *
unaffected

Default status
affected

26.2-18 (rpm) before *
unaffected

Default status
unaffected

Default status
affected

26.4.11-1 (rpm) before *
unaffected

Default status
affected

26.4-14 (rpm) before *
unaffected

Default status
affected

26.4-14 (rpm) before *
unaffected

Default status
unaffected

Timeline

2026-03-23:Reported to Red Hat.
2026-04-02:Made public.

Credits

Red Hat would like to thank Slvrqn for reporting this issue.

References

access.redhat.com/errata/RHSA-2026:6475 (RHSA-2026:6475) vendor-advisory

access.redhat.com/errata/RHSA-2026:6476 (RHSA-2026:6476) vendor-advisory

access.redhat.com/errata/RHSA-2026:6477 (RHSA-2026:6477) vendor-advisory

access.redhat.com/errata/RHSA-2026:6478 (RHSA-2026:6478) vendor-advisory

access.redhat.com/security/cve/CVE-2026-4634 vdb-entry

bugzilla.redhat.com/show_bug.cgi?id=2450250 (RHBZ#2450250) issue-tracking

cve.org (CVE-2026-4634)

nvd.nist.gov (CVE-2026-4634)

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