Vulnerability · Published Apr 6, 2026 · Assigned by redhat
CVE-2026-37977Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim
Low 3.7
In plain English
A low-severity security flaw in Red Hat build of Keycloak 26.4 from Red Hat. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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: ["*"]`.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Maven | org.keycloak:keycloak-services | 26.4.13 | GHSA-5v8v-xvjv-57x7 |
| Maven | org.keycloak:keycloak-services | 26.6.3 | GHSA-5v8v-xvjv-57x7 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Red Hat | Red Hat build of Keycloak 26.4 | see references |
| Red Hat | Red Hat build of Keycloak 26.4 | see references |
| Red Hat | Red Hat build of Keycloak 26.4 | see references |
| Red Hat | Red Hat build of Keycloak 26.4.13 | see references |
| Red Hat | Red Hat build of Keycloak 26.6 | see references |
| Red Hat | Red Hat build of Keycloak 26.6 | see references |
| Red Hat | Red Hat build of Keycloak 26.6 | see references |
| Red Hat | Red Hat build of Keycloak 26.6.3 | see references |
Weakness: CWE-346 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
References
- RHSA-2026:25097 vendor-advisory, x_refsource_REDHAT
- RHSA-2026:25098 vendor-advisory, x_refsource_REDHAT
- RHSA-2026:30049 vendor-advisory, x_refsource_REDHAT
- RHSA-2026:30050 vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/security/cve/CVE-2026-37977 vdb-entry, x_refsource_REDHAT
- RHBZ#2455324 issue-tracking, x_refsource_REDHAT