---
id: CVE-2026-4634
title: A flaw was found in Keycloak
summary: >-
  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…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-1050
vendor: redhat
product: build_of_keycloak
affected:
  - build_of_keycloak
  - build_of_keycloak = 26.2
  - build_of_keycloak = 26.2.15
  - build_of_keycloak = 26.4
  - build_of_keycloak = 26.4.11
published: '2026-04-02'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T15:17:26.507'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-4634'
references:
  - url: 'https://access.redhat.com/errata/RHSA-2026:6475'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:6476'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:6477'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:6478'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/security/cve/CVE-2026-4634'
    label: secalert@redhat.com
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2450250'
    label: secalert@redhat.com
  - url: 'https://access.redhat.com/errata/RHSA-2026:6475'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6476'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6477'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/errata/RHSA-2026:6478'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://access.redhat.com/security/cve/CVE-2026-4634'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2450250'
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-4634.json
    label: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-04-03T17:22:51.847497Z'
epss: 0.00709
epssPercentile: 0.51631
ingestedAt: '2026-09-29T16:39:33.224Z'
---

## Overview

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.

## Affected

- `build_of_keycloak`
- `build_of_keycloak = 26.2`
- `build_of_keycloak = 26.2.15`
- `build_of_keycloak = 26.4`
- `build_of_keycloak = 26.4.11`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.