EUVD-2026-19201
GHSA-5v8v-xvjv-57x7
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Lifecycle Timeline
3Tags
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: ["*"]`.
Analysis
CORS header injection in Keycloak's User-Managed Access token endpoint allows remote attackers to reflect attacker-controlled origin values before JWT signature validation, potentially exposing low-sensitivity authorization error responses when clients are misconfigured with wildcard origin permissions. The vulnerability requires high attack complexity and affects only clients explicitly configured with webOrigins set to "*", resulting in a low-severity information disclosure with limited real-world exploitability.
Sign in for full analysis, threat intelligence, and remediation guidance.
Priority Score
Share
External POC / Exploit Code
Leaving vuln.today