CVE-2026-37977

MEDIUM EPSS 16.5%

Published Apr 6, 20262mo ago · Modified Jun 17, 20261w ago

5.3 CVSS 3.1

Medium

Published Apr 6, 2026 2mo ago

Last Modified Jun 17, 2026 1w ago

Description

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 Details

Base Score

5.3

Exploitability

3.9

Impact

1.4

Vector string

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack Vector Network

Attack Complexity Low

Privileges Required None

User Interaction None

Scope Unchanged

Confidentiality Low

Integrity None

Availability None

Threat Intelligence

EPSS Exploit Probability

16.5% percentile

Exploit & Patch Status

No Known Exploit

No Patch Available

Weaknesses 1

CWE-346

Affected Products 1

Vendor	Product	Version	Range
redhat	build_of_keycloak	*	any

References 4

access.redhat.com https://access.redhat.com/errata/RHSA-2026:25097
access.redhat.com https://access.redhat.com/errata/RHSA-2026:25098
access.redhat.com https://access.redhat.com/security/cve/CVE-2026-37977

Vendor Advisory
bugzilla.redhat.com https://bugzilla.redhat.com/show_bug.cgi?id=2455324

Issue TrackingVendor Advisory

Remediation

No remediation data recorded yet

Check vendor advisories and the NVD entry for patch availability.