CVE-2026-4634

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

State: Published
Severity: 7.5 High
Published: Apr 2, 2026
Updated: Oct 6, 2026
Reserved: Mar 23, 2026

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.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	redhat
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	redhat-SADP

Weaknesses

CWE-1050 Excessive Platform Resource Consumption within a Loop

Affected Products

Product	Versions
Red Hat build of Keycloak 26.2Red Hat	26.2.15-1 and laterNot affected
Red Hat build of Keycloak 26.2Red Hat	26.2-18 and laterNot affected
Red Hat build of Keycloak 26.2Red Hat	26.2-18 and laterNot affected
Red Hat build of Keycloak 26.2.15Red Hat
Red Hat build of Keycloak 26.4Red Hat	26.4.11-1 and laterNot affected
Red Hat build of Keycloak 26.4Red Hat	26.4-14 and laterNot affected
Red Hat build of Keycloak 26.4Red Hat	26.4-14 and laterNot affected
Red Hat build of Keycloak 26.4.11Red Hat
Red Hat Single Sign-On 7.6.13Red Hat
Red Hat Single Sign-On 7.6 for RHEL 7Red Hat	0:18.0.20-1.redhat_00001.1.el7sso and laterNot affected
Red Hat Single Sign-On 7.6 for RHEL 8Red Hat	0:18.0.20-1.redhat_00001.1.el8sso and laterNot affected
Red Hat Single Sign-On 7.6 for RHEL 9Red Hat	0:18.0.20-1.redhat_00001.1.el9sso and laterNot affected
RHEL-8 based Middleware ContainersRed Hat	7.6-85 and laterNot affected

References

RHSA-2026:6475vendor-advisory
RHSA-2026:6476vendor-advisory
RHSA-2026:6477vendor-advisory
RHSA-2026:6478vendor-advisory
RHSA-2026:76128vendor-advisory
RHSA-2026:76129vendor-advisory
RHSA-2026:76130vendor-advisory
RHSA-2026:76132vendor-advisory
RHSA-2026:76134vendor-advisory
https://access.redhat.com/security/cve/CVE-2026-4634vdb-entry
RHBZ#2450250issue-tracking
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4634.json

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