CVE-2026-37977: Keycloak services Keycloak Vulnerable To Information Disclosure Vulnerability

LOW
Advisory Identifier: GHSA-5v8v-xvjv-57x7
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CVSS 3.7
CWE-346
Published
Advisory Summary

CVE-2026-37977 is a LOW (CVSS 3.7) keycloak vulnerable to information disclosure vulnerability (CWE-346: Origin Validation Error) affecting Keycloak services libraries in the Maven ecosystem. The issue involves keycloak vulnerable to information disclosure via cors header injection due to unvalidated jwt azp claim. Remediation is available by upgrading affected packages to version 26.4.13, 26.6.3.

CVE-2026-37977 at a Glance

CVE Identifier CVE-2026-37977
GHSA Identifier GHSA-5v8v-xvjv-57x7
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-346: Origin Validation Error
Affected Product Keycloak services
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 3.7

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

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

How to Fix CVE-2026-37977

To remediate this vulnerability, upgrade all affected Keycloak services 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: 26.4.13 
<dependency>
    <groupId>org.keycloak</groupId>
    <artifactId>keycloak-services</artifactId>
    <version>26.4.13</version>
</dependency>
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-2026-37977, 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 services in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 26.4.13), 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-346: Origin Validation Error, where the product does not properly verify that the source of data or communication is valid. In Keycloak services, 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. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: ["*"]`.

CVE-2026-37977 Affected Keycloak services Versions

2 component(s)
Fixed Versions:
26.4.1326.6.3
Product / Package Ecosystem Affected Versions Fixed Version
org.keycloak:keycloak-services
maven/org.keycloak/keycloak-services
Maven
< 26.4.13
26.4.13
org.keycloak:keycloak-services
maven/org.keycloak/keycloak-services
Maven
≥ 26.5.0
< 26.6.3
26.6.3

References

NVD — CVE-2026-37977 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-37977
Keycloak services Source Repository REPOSITORY
https://github.com/keycloak/keycloak/issues/48036
Keycloak services Source Repository REPOSITORY
https://github.com/keycloak/keycloak/pull/49512
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/1439bd58a9f25b0d28d0400015f49f35f227ce04
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/461ce79a6cd6bfef7ca7fa41da287a3127f47ae4
Security Fix Commit FIX COMMIT
https://github.com/keycloak/keycloak/commit/ad34724a5d1ba8b6edf7a2c8c83826b1c20539e7
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 services Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-37977
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2455324
Keycloak services Source Repository REPOSITORY
https://github.com/keycloak/keycloak

Frequently Asked Questions

What is CVE-2026-37977?
CVE-2026-37977 is a security vulnerability in Keycloak services involving Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim under CWE-346: Origin Validation Error.
Which Keycloak services versions are affected?
Affected versions include releases prior to 26.4.13, 26.6.3 across affected packages: org.keycloak:keycloak-services.
What version fixes CVE-2026-37977?
Upgrading to 26.4.13, 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 26.4.13, 26.6.3. Upgrade your dependency to 26.4.13, 26.6.3 or later.
What is the CVSS score of CVE-2026-37977?
CVE-2026-37977 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.
What CWE is associated with CVE-2026-37977?
CVE-2026-37977 is classified under CWE-346: Origin Validation Error (The product does not properly verify that the source of data or communication is valid.).
How can I check Maven dependencies for CVE-2026-37977?
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-5v8v-xvjv-57x7",
  "modified" : "2026-07-15T18:38:09Z",
  "published" : "2026-04-06T09:31:42Z",
  "aliases" : [ "CVE-2026-37977" ],
  "summary" : "Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim",
  "details" : "A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the `azp` claim from a client-supplied JSON Web Token (JWT) is used to set the `Access-Control-Allow-Origin` header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled `azp` value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with `webOrigins: [\"*\"]`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.keycloak:keycloak-services"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
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      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.keycloak:keycloak-services"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "26.5.0"
      }, {
        "fixed" : "26.6.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-37977"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/issues/48036"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/pull/49512"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/1439bd58a9f25b0d28d0400015f49f35f227ce04"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/461ce79a6cd6bfef7ca7fa41da287a3127f47ae4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/keycloak/keycloak/commit/ad34724a5d1ba8b6edf7a2c8c83826b1c20539e7"
  }, {
    "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-2026-37977"
  }, {
    "type" : "WEB",
    "url" : "https://bugzilla.redhat.com/show_bug.cgi?id=2455324"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/keycloak/keycloak"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-346" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-08T00:08:09Z",
    "nvd_published_at" : "2026-04-06T09:16:17Z"
  }
}