CVE-2026-4634

HIGH 7.5

Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters

CVSS Score

7.5

EPSS Score

0.1%

EPSS Percentile

21th

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.

CWE	CWE-1050
Vendor	red hat
Product	red hat build of keycloak 26.2
Published	Apr 2, 2026
Last Updated	Apr 3, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Affected Versions

Red Hat / Red Hat build of Keycloak 26.2

All versions affected

Red Hat / Red Hat build of Keycloak 26.2

All versions affected

Red Hat / Red Hat build of Keycloak 26.2

All versions affected

Red Hat / Red Hat build of Keycloak 26.2.15

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

All versions affected

Red Hat / Red Hat build of Keycloak 26.4.11

All versions affected

References

NVD ↗ CVE.org ↗ EPSS Data ↗

access.redhat.com: https://access.redhat.com/errata/RHSA-2026:6475 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:6476 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:6477 access.redhat.com: https://access.redhat.com/errata/RHSA-2026:6478 access.redhat.com: https://access.redhat.com/security/cve/CVE-2026-4634 bugzilla.redhat.com: https://bugzilla.redhat.com/show_bug.cgi?id=2450250

Credits

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