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 3.1
- 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N - EPSS
- 0.3% chance of exploitation in the next 30 days; higher than 16% of CVEs (scores of 2026-10-26)
- CWE
- CWE-346
- Published
- Modified
- Record from
- the NVD, synced
Affected
- redhat:build_of_keycloak
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-5v8v-xvjv-57x7 | Maven | org.keycloak:keycloak-services | <26.4.13 | 26.4.13 |
| GHSA-5v8v-xvjv-57x7 | Maven | org.keycloak:keycloak-services | >=26.5.0 <26.6.3 | 26.6.3 |