CVE-2026-37977

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: ["*"]`.

CVSS v3 3.7 LOW

3.7^/10

CVSS v3 : LOW

Vector :

Exploitability : 2.2 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://access.redhat.com/security/cve/CVE-2026-37977	Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2455324	Issue Tracking Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:-:*:*:*

History

24 Apr 2026, 15:39

Type	Values Removed	Values Added
First Time		Redhat Redhat build Of Keycloak
CPE		cpe:2.3:a:redhat:build_of_keycloak:-::::-:::
References	~~() https://access.redhat.com/security/cve/CVE-2026-37977 -~~	() https://access.redhat.com/security/cve/CVE-2026-37977 - Vendor Advisory
References	~~() https://bugzilla.redhat.com/show_bug.cgi?id=2455324 -~~	() https://bugzilla.redhat.com/show_bug.cgi?id=2455324 - Issue Tracking, Vendor Advisory

06 Apr 2026, 09:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-04-06 09:16

Updated : 2026-04-24 15:39

NVD link : CVE-2026-37977

Mitre link : CVE-2026-37977

CVE.ORG link : CVE-2026-37977

JSON object : View

Products Affected

redhat

build_of_keycloak

CWE

CWE-346

Origin Validation Error

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