FKIE_CVE-2026-37977

Vulnerability from fkie_nvd - Published: 2026-04-06 09:16 - Updated: 2026-04-24 15:39
Severity
3.7 (Low) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
5.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Summary
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: ["*"]`.
References
secalert@redhat.comhttps://access.redhat.com/security/cve/CVE-2026-37977Vendor Advisory
secalert@redhat.comhttps://bugzilla.redhat.com/show_bug.cgi?id=2455324Issue Tracking, Vendor Advisory
Impacted products
Vendor Product Version
redhat build_of_keycloak -
To clipboard 

{
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    {
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              "criteria": "cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:-:*:*:*",
              "matchCriteriaId": "E5C930CB-4EAD-497B-A44B-D880F2A1F85B",
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak\u0027s 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: [\"*\"]`."
    }
  ],
  "id": "CVE-2026-37977",
  "lastModified": "2026-04-24T15:39:21.883",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 3.7,
          "baseSeverity": "LOW",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N",
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          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
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  "published": "2026-04-06T09:16:17.850",
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      "tags": [
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  "sourceIdentifier": "secalert@redhat.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
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          "lang": "en",
          "value": "CWE-346"
        }
      ],
      "source": "secalert@redhat.com",
      "type": "Primary"
    }
  ]
}


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