CVE-2026-4634: Keycloak Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-h4wv-g838-66g3
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CVSS 7.5
CWE-1050
Published
Advisory Summary

CVE-2026-4634 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-1050: Excessive Platform Resource Consumption within a Loop) affecting Keycloak libraries in the Maven ecosystem. The issue involves application-level dos via scope processing. Remediation is available by upgrading affected packages to version 26.5.7.

CVE-2026-4634 at a Glance

CVE Identifier CVE-2026-4634
GHSA Identifier GHSA-h4wv-g838-66g3
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-1050: Excessive Platform Resource Consumption within a Loop
Affected Product Keycloak
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-4634

To remediate this vulnerability, upgrade all affected Keycloak dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

org.keycloak:keycloak-services fixed: 26.5.7 
<dependency>
    <groupId>org.keycloak</groupId>
    <artifactId>keycloak-services</artifactId>
    <version>26.5.7</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=org.keycloak

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-4634, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.keycloak

Analyze the terminal output to locate any version of Keycloak in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 26.5.7), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.keycloak command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1050: Excessive Platform Resource Consumption within a Loop, where the product has a loop body or loop condition that contains a control element that directly or indirectly consumes platform resources, e.g. messaging, sessions, locks, or file descriptors. In Keycloak, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

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.

CVE-2026-4634 Affected Keycloak Versions

1 component(s)
Fixed Versions:
26.5.7
Product / Package Ecosystem Affected Versions Fixed Version
org.keycloak:keycloak-services
maven/org.keycloak/keycloak-services
Maven
< 26.5.7
26.5.7

References

NVD — CVE-2026-4634 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4634
Keycloak Source Repository REPOSITORY
https://github.com/keycloak/keycloak/issues/47716
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/b455ee4f28abb6f2120aff72fd179589cc5267a0
access.redhat.com/errata/rhsa-2026:64... WEB
https://access.redhat.com/errata/RHSA-2026:6475
access.redhat.com/errata/rhsa-2026:64... WEB
https://access.redhat.com/errata/RHSA-2026:6476
access.redhat.com/errata/rhsa-2026:64... WEB
https://access.redhat.com/errata/RHSA-2026:6477
access.redhat.com/errata/rhsa-2026:64... WEB
https://access.redhat.com/errata/RHSA-2026:6478
Keycloak Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-4634
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2450250
Keycloak Source Repository REPOSITORY
https://github.com/keycloak/keycloak

Frequently Asked Questions

What is CVE-2026-4634?
CVE-2026-4634 is a security vulnerability in Keycloak involving Application-Level DoS via Scope Processing under CWE-1050: Excessive Platform Resource Consumption within a Loop.
Which Keycloak versions are affected?
Affected versions include releases prior to 26.5.7 across affected packages: org.keycloak:keycloak-services.
What version fixes CVE-2026-4634?
Upgrading to 26.5.7 (or the latest patched release for your respective branch) resolves the vulnerability.
Is keycloak-services affected?
Yes, org.keycloak:keycloak-services is affected in releases prior to 26.5.7. Upgrade your dependency to 26.5.7 or later.
What is the CVSS score of CVE-2026-4634?
CVE-2026-4634 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-4634?
CVE-2026-4634 is classified under CWE-1050: Excessive Platform Resource Consumption within a Loop (The product has a loop body or loop condition that contains a control element that directly or indirectly consumes platform resources, e.g. messaging, sessions, locks, or file descriptors.).
How can I check Maven dependencies for CVE-2026-4634?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.keycloak'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-h4wv-g838-66g3",
  "modified" : "2026-04-04T06:00:47Z",
  "published" : "2026-04-02T15:31:39Z",
  "aliases" : [ "CVE-2026-4634" ],
  "summary" : "Keycloak: Application-Level DoS via Scope Processing",
  "details" : "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.keycloak:keycloak-services"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "26.5.7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-4634"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/issues/47716"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/b455ee4f28abb6f2120aff72fd179589cc5267a0"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:6475"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:6476"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:6477"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:6478"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-4634"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2450250"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/keycloak/keycloak"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1050" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:00:47Z",
    "nvd_published_at" : "2026-04-02T13:16:27Z"
  }
}