CVE-2026-37977: Origin Validation Error in Red Hat Red Hat Build of Keycloak
CVE-2026-37977 is a low-severity vulnerability in Red Hat Build of Keycloak involving a Cross-Origin Resource Sharing (CORS) header injection at the User-Managed Access (UMA) token endpoint. The vulnerability arises because the 'azp' claim from a client-supplied JWT is used to set the Access-Control-Allow-Origin header before the JWT signature is validated. This can cause an attacker-controlled origin to be reflected even if the grant is rejected, potentially exposing low-sensitivity information from authorization server error responses. The issue only manifests when a client is misconfigured with 'webOrigins' set to allow all origins ('*'). No official patch or remediation level is currently provided by Red Hat, and no known exploits are reported in the wild.
AI Analysis
Technical Summary
This vulnerability in Red Hat Build of Keycloak allows a remote attacker to inject a malicious origin into the Access-Control-Allow-Origin header via the 'azp' claim in a JWT at the UMA token endpoint. The flaw occurs because the header is set before the JWT signature is validated, enabling reflection of attacker-controlled values even if the token is ultimately rejected. This can weaken origin isolation and expose low-sensitivity error response information, but only if the client is configured with 'webOrigins' set to '*'. The CVSS score is 3.7 (low severity), reflecting limited impact and the requirement for specific client misconfiguration. Red Hat has published an advisory but has not indicated an official fix or patch availability as of the publication date.
Potential Impact
The impact is limited to the exposure of low-sensitivity information from authorization server error responses due to weakened origin isolation caused by CORS header injection. This does not allow token acceptance or privilege escalation. The vulnerability requires a client misconfiguration ('webOrigins' set to '*') to be exploitable. There are no known exploits in the wild, and the overall severity is low.
Mitigation Recommendations
Patch status is not yet confirmed — check the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-37977 for current remediation guidance. Until an official fix is available, avoid configuring clients with 'webOrigins' set to '*', as this misconfiguration enables the vulnerability. No other specific mitigations are indicated by the vendor advisory.
CVE-2026-37977: Origin Validation Error in Red Hat Red Hat Build of Keycloak
Description
CVE-2026-37977 is a low-severity vulnerability in Red Hat Build of Keycloak involving a Cross-Origin Resource Sharing (CORS) header injection at the User-Managed Access (UMA) token endpoint. The vulnerability arises because the 'azp' claim from a client-supplied JWT is used to set the Access-Control-Allow-Origin header before the JWT signature is validated. This can cause an attacker-controlled origin to be reflected even if the grant is rejected, potentially exposing low-sensitivity information from authorization server error responses. The issue only manifests when a client is misconfigured with 'webOrigins' set to allow all origins ('*'). No official patch or remediation level is currently provided by Red Hat, and no known exploits are reported in the wild.
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability in Red Hat Build of Keycloak allows a remote attacker to inject a malicious origin into the Access-Control-Allow-Origin header via the 'azp' claim in a JWT at the UMA token endpoint. The flaw occurs because the header is set before the JWT signature is validated, enabling reflection of attacker-controlled values even if the token is ultimately rejected. This can weaken origin isolation and expose low-sensitivity error response information, but only if the client is configured with 'webOrigins' set to '*'. The CVSS score is 3.7 (low severity), reflecting limited impact and the requirement for specific client misconfiguration. Red Hat has published an advisory but has not indicated an official fix or patch availability as of the publication date.
Potential Impact
The impact is limited to the exposure of low-sensitivity information from authorization server error responses due to weakened origin isolation caused by CORS header injection. This does not allow token acceptance or privilege escalation. The vulnerability requires a client misconfiguration ('webOrigins' set to '*') to be exploitable. There are no known exploits in the wild, and the overall severity is low.
Mitigation Recommendations
Patch status is not yet confirmed — check the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-37977 for current remediation guidance. Until an official fix is available, avoid configuring clients with 'webOrigins' set to '*', as this misconfiguration enables the vulnerability. No other specific mitigations are indicated by the vendor advisory.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- redhat
- Date Reserved
- 2026-04-06T07:48:39.721Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://access.redhat.com/security/cve/CVE-2026-37977","vendor":"Red Hat"}]
Threat ID: 69d372ac0a160ebd9293290b
Added to database: 4/6/2026, 8:45:32 AM
Last enriched: 4/6/2026, 9:00:43 AM
Last updated: 4/6/2026, 10:04:01 AM
Views: 6
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