CVE-2026-37977
Redhat Build Of Keycloak
Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:NSummary
CVE-2026-37977 is a low-severity Origin Validation Error (CWE-346) vulnerability in Redhat Build Of Keycloak. Its CVSS base score is 3.7 (Low).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 17th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-19201
Vulnerability Data
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)…
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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: ["*"]`.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
CORS header injection in public-facing Keycloak UMA endpoint enables exploitation of a web application for limited information disclosure.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Requires validation of untrusted JWT claims (azp) before they are used to construct CORS headers.
Enforces that access-control decisions and header generation occur only after successful JWT signature validation.
Controls information flow by restricting which origins may receive error responses containing authorization data.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Authentication directly verifies the source of users/services/hardware, mitigating origin validation failures.
Verifying identity assertions enforces origin validation for conveyed claims.
Documenting authorized flows supports origin validation by defining expected sources.
Protecting networks from unauthorized access requires origin checks on communication sources.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Network security controls enforce origin validation at network boundaries.
Security of network services includes validating the authenticity of service endpoints.
Network segregation reduces exposure but does not directly validate origins.
Application security requirements explicitly call for origin validation of inputs and communications.
Secure architecture principles encourage origin checks but do not mandate them.
Secure coding practices include implementing proper origin validation to prevent spoofing.