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CVE-2026-37977— Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim

Quick assessment

Affected
Red Hat Red Hat build of Keycloak 26.4
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Keycloak是Keycloak开源的一种开源身份和访问管理解决方案。 Keycloak存在访问控制错误漏洞，该漏洞源于用户管理访问令牌端点存在跨域资源共享标头注入，可能导致授权服务器错误响应中的低敏感性信息泄露。

CVSS 3.7 · Low EPSS 0.27% · P18

Affected Version Matrix 8

VendorProduct Version RangeStatus
Red Hat Red Hat build of Keycloak 26.4 26.4.13-1< * unaffected
26.4-19< * unaffected
26.4-19< * unaffected
Red Hat Red Hat build of Keycloak 26.4.13 any unaffected
Red Hat Red Hat build of Keycloak 26.6 26.6.3-3< * unaffected
26.6-6< * unaffected
26.6-6< * unaffected
Red Hat Red Hat build of Keycloak 26.6.3 any unaffected
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I. Basic Information for CVE-2026-37977

Vulnerability Information
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Vulnerability Title
Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim
Source: CVE Program / CVE List V5
Vulnerability 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: ["*"]`.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
源验证错误
Source: CVE Program / CVE List V5
Vulnerability Title
Keycloak 访问控制错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Keycloak是Keycloak开源的一种开源身份和访问管理解决方案。 Keycloak存在访问控制错误漏洞，该漏洞源于用户管理访问令牌端点存在跨域资源共享标头注入，可能导致授权服务器错误响应中的低敏感性信息泄露。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Red Hat Red Hat build of Keycloak 26.4 26.4.13-1 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4 26.4-19 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4 26.4-19 ~ * cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.4.13 - cpe:/a:redhat:build_keycloak:26.4::el9
Red Hat Red Hat build of Keycloak 26.6 26.6.3-3 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6 26.6-6 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6 26.6-6 ~ * cpe:/a:redhat:build_keycloak:26.6::el9
Red Hat Red Hat build of Keycloak 26.6.3 - cpe:/a:redhat:build_keycloak:26.6::el9

II. Public POCs for CVE-2026-37977

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III. Intelligence Information for CVE-2026-37977

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Vendor Advisories for CVE-2026-37977 (3)

Other References for CVE-2026-37977 (2)

Same Patch Batch · Red Hat · 2026-04-06 · 3 CVEs total

CVE-2026-5673 5.6 MEDIUM Libtheora: libtheora: denial of service or information disclosure via malformed avi file p
CVE-2026-5704 5.0 MEDIUM Tar: tar: hidden file injection via crafted archives

IV. Related Vulnerabilities

Same product: Red Hat build of Keycloak 26.4
Same vendor: Red Hat
Same weakness: CWE-346

V. Comments for CVE-2026-37977

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