CVE-2026-9087: Keycloak Insufficient Verification Proof Scoping Enables Vulnerability

MODERATE
Advisory Identifier: GHSA-m6qj-3mpp-57v8
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CVSS 6.4
CWE-639
Published
Advisory Summary

CVE-2026-9087 is a MODERATE (CVSS 6.4) insufficient verification proof scoping enables vulnerability (CWE-639: Authorization Bypass Through User-Controlled Key) affecting Keycloak libraries in the Maven ecosystem. The issue involves insufficient verification proof scoping enables identity provider account linking attack and account compromise. Remediation is available by upgrading affected packages to version 26.6.3.

CVE-2026-9087 at a Glance

CVE Identifier CVE-2026-9087
GHSA Identifier GHSA-m6qj-3mpp-57v8
Severity MODERATE
CVSS v3.1 Base Score 6.4
CWE Classification CWE-639: Authorization Bypass Through User-Controlled Key
Affected Product Keycloak
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.4

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

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

How to Fix CVE-2026-9087

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: 26.6.3 
<dependency>
    <groupId>org.keycloak</groupId>
    <artifactId>keycloak-services</artifactId>
    <version>26.6.3</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-2026-9087, 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 26.6.3), 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-639: Authorization Bypass Through User-Controlled Key, where the system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. 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. The cross-session verification proof is keyed only by (local userId, idpAlias) and is not bound to the upstream identity that was actually verified, so a second upstream account on the same IdP can consume it and get linked to the victim's local account.

CVE-2026-9087 Affected Keycloak Versions

1 component(s)
Fixed Versions:
26.6.3
Product / Package Ecosystem Affected Versions Fixed Version
org.keycloak:keycloak-services
maven/org.keycloak/keycloak-services
Maven
< 26.6.3
26.6.3

References

NVD — CVE-2026-9087 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-9087
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/37dabf59d0b5ca3e5b3b272bcd3b2580e67b94dd
access.redhat.com/errata/rhsa-2026:25... WEB
https://access.redhat.com/errata/RHSA-2026:25097
access.redhat.com/errata/rhsa-2026:25... WEB
https://access.redhat.com/errata/RHSA-2026:25098
access.redhat.com/errata/rhsa-2026:30... WEB
https://access.redhat.com/errata/RHSA-2026:30049
access.redhat.com/errata/rhsa-2026:30... WEB
https://access.redhat.com/errata/RHSA-2026:30050
Keycloak Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-9087
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2480172
Keycloak Source Repository REPOSITORY
https://github.com/keycloak/keycloak
Keycloak Release RELEASE
https://github.com/keycloak/keycloak/releases/tag/26.6.3

Frequently Asked Questions

What is CVE-2026-9087?
CVE-2026-9087 is a security vulnerability in Keycloak involving Insufficient verification proof scoping enables identity provider account linking attack and account compromise under CWE-639: Authorization Bypass Through User-Controlled Key.
Which Keycloak versions are affected?
Affected versions include releases prior to 26.6.3 across affected packages: org.keycloak:keycloak-services.
What version fixes CVE-2026-9087?
Upgrading to 26.6.3 (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 26.6.3. Upgrade your dependency to 26.6.3 or later.
What is the CVSS score of CVE-2026-9087?
CVE-2026-9087 has a CVSS v3.1 base score of 6.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-9087?
CVE-2026-9087 is classified under CWE-639: Authorization Bypass Through User-Controlled Key (The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.).
How can I check Maven dependencies for CVE-2026-9087?
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-m6qj-3mpp-57v8",
  "modified" : "2026-06-26T09:30:45Z",
  "published" : "2026-05-20T18:31:36Z",
  "aliases" : [ "CVE-2026-9087" ],
  "summary" : "Keycloak: Insufficient verification proof scoping enables identity provider account linking attack and account compromise",
  "details" : "A flaw was found in Keycloak. The cross-session verification proof is keyed only by (local userId,\nidpAlias) and is not bound to the upstream identity that was actually verified, so a second upstream account on the same IdP can consume it and get linked to the victim's local account.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.keycloak:keycloak-services"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "26.6.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9087"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/37dabf59d0b5ca3e5b3b272bcd3b2580e67b94dd"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:25097"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:25098"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:30049"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/errata/RHSA-2026:30050"
  }, {
    "type" : "WEB",
    "url" : "https://access.redhat.com/security/cve/CVE-2026-9087"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2480172"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/keycloak/keycloak"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/releases/tag/26.6.3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-639" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-11T16:40:55Z",
    "nvd_published_at" : "2026-05-20T17:16:32Z"
  }
}