CVE-2026-4636: Keycloak Remote Code Execution Vulnerability

HIGH
Advisory Identifier: GHSA-f2hx-5fx3-hmcv
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CVSS 8.1
CWE-551
Published
Advisory Summary

CVE-2026-4636 is a HIGH (CVSS 8.1) remote code execution vulnerability (CWE-551: Incorrect Behavior Order: Authorization Before Parsing and Canonicalization) affecting Keycloak libraries in the Maven ecosystem. The issue involves uma policy resource injection allows unauthorized cross-user permission grants. Remediation is available by upgrading affected packages to version 26.5.7.

CVE-2026-4636 at a Glance

CVE Identifier CVE-2026-4636
GHSA Identifier GHSA-f2hx-5fx3-hmcv
Severity HIGH
CVSS v3.1 Base Score 8.1
CWE Classification CWE-551: Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
Affected Product Keycloak
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 8.1

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

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

How to Fix CVE-2026-4636

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-2026-4636, 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-551: Incorrect Behavior Order: Authorization Before Parsing and Canonicalization, where if a web server does not fully parse requested urls before it examines them for authorization, it may be possible for an attacker to bypass authorization protection. 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 authenticated user with the uma_protection role can bypass User-Managed Access (UMA) policy validation. This allows the attacker to include resource identifiers owned by other users in a policy creation request, even if the URL path specifies an attacker-owned resource. Consequently, the attacker gains unauthorized permissions to victim-owned resources, enabling them to obtain a Requesting Party Token (RPT) and access sensitive information or perform unauthorized actions.

CVE-2026-4636 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

Keycloak Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-4636
NVD — CVE-2026-4636 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4636
Keycloak Source Repository REPOSITORY
https://github.com/keycloak/keycloak/issues/47717
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/995832f8b74b02833d106c8788bb7a78634aa725
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
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2450251
Keycloak Source Repository REPOSITORY
https://github.com/keycloak/keycloak

Frequently Asked Questions

What is CVE-2026-4636?
CVE-2026-4636 is a security vulnerability in Keycloak involving UMA Policy Resource Injection Allows Unauthorized Cross-User Permission Grants under CWE-551: Incorrect Behavior Order: Authorization Before Parsing and Canonicalization.
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-2026-4636?
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-2026-4636?
CVE-2026-4636 has a CVSS v3.1 base score of 8.1 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-4636?
CVE-2026-4636 is classified under CWE-551: Incorrect Behavior Order: Authorization Before Parsing and Canonicalization (If a web server does not fully parse requested URLs before it examines them for authorization, it may be possible for an attacker to bypass authorization protection.).
How can I check Maven dependencies for CVE-2026-4636?
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-f2hx-5fx3-hmcv",
  "modified" : "2026-04-04T06:00:14Z",
  "published" : "2026-04-02T15:31:39Z",
  "aliases" : [ "CVE-2026-4636" ],
  "summary" : "Keycloak: UMA Policy Resource Injection Allows Unauthorized Cross-User Permission Grants",
  "details" : "A flaw was found in Keycloak. An authenticated user with the uma_protection role can bypass User-Managed Access (UMA) policy validation. This allows the attacker to include resource identifiers owned by other users in a policy creation request, even if the URL path specifies an attacker-owned resource. Consequently, the attacker gains unauthorized permissions to victim-owned resources, enabling them to obtain a Requesting Party Token (RPT) and access sensitive information or perform unauthorized actions.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "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-2026-4636"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/issues/47717"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/995832f8b74b02833d106c8788bb7a78634aa725"
  }, {
    "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-2026-4636"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2450251"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/keycloak/keycloak"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-551" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-04T06:00:14Z",
    "nvd_published_at" : "2026-04-02T13:16:27Z"
  }
}