CVE-2026-4634Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters

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.

Timeline

Scores

EPSS (exploitation in 30 days)

0.64% · top 49% of all CVEs (14 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: yes · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.

Affected products

• Red Hat · Red Hat build of Keycloak 26.2

  • unaffected 26.2.15-1 – < *

• Red Hat · Red Hat build of Keycloak 26.2

  • unaffected 26.2-18 – < *

• Red Hat · Red Hat build of Keycloak 26.2

  • unaffected 26.2-18 – < *

• Red Hat · Red Hat build of Keycloak 26.2.15

  All versions: unaffected

• Red Hat · Red Hat build of Keycloak 26.4

  • unaffected 26.4.11-1 – < *

• Red Hat · Red Hat build of Keycloak 26.4

  • unaffected 26.4-14 – < *

• Red Hat · Red Hat build of Keycloak 26.4

  • unaffected 26.4-14 – < *

• Red Hat · Red Hat build of Keycloak 26.4.11

  All versions: unaffected

• Red Hat · Red Hat Single Sign-On 7.6.13

  All versions: unaffected

• Red Hat · Red Hat Single Sign-On 7.6 for RHEL 7

  • unaffected 0:18.0.20-1.redhat_00001.1.el7sso – < *

• Red Hat · Red Hat Single Sign-On 7.6 for RHEL 8

  • unaffected 0:18.0.20-1.redhat_00001.1.el8sso – < *

• Red Hat · Red Hat Single Sign-On 7.6 for RHEL 9

  • unaffected 0:18.0.20-1.redhat_00001.1.el9sso – < *

• Red Hat · RHEL-8 based Middleware Containers

  • unaffected 7.6-85 – < *

Affected packages

From reviewed advisories of the GitHub Advisory Database.

• Mavenorg.keycloak:keycloak-servicesGHSA-h4wv-g838-66g3 (opens in a new tab)

What to do

Workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-18212 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisory GHSA-h4wv-g838-66g3 (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-4634](https://cveledger.app/badge/CVE-2026-4634.svg)](https://cveledger.app/cve/CVE-2026-4634)

Record last updated 6 Oct 2026, 16:58 UTC.