CVE-2026-3911 is a security vulnerability identified in the Red Hat Build of Keycloak, an open-source identity and access management solution. The flaw exists in the UserResource component, which handles user-related administrative functions. Specifically, an authenticated user possessing the 'view-users' role can exploit this vulnerability by accessing a particular administrative endpoint designed to retrieve user attributes. Due to improper access control or filtering, this endpoint returns user attributes that were configured to be hidden, thereby exposing sensitive personal information that should remain confidential. The vulnerability does not require user interaction and is exploitable remotely over the network (AV:N) with low attack complexity (AC:L), but it does require the attacker to have authenticated privileges (PR:H). The impact is limited to confidentiality (C:L), with no effect on integrity or availability. The vulnerability was published on March 11, 2026, with no known exploits in the wild at the time of reporting. The affected versions are not explicitly listed, but the issue pertains to Red Hat's distribution of Keycloak. This vulnerability highlights a misconfiguration or coding oversight in access control enforcement within Keycloak's administrative API endpoints.

The primary impact of CVE-2026-3911 is unauthorized disclosure of sensitive user attributes that were intended to be hidden, potentially including personally identifiable information (PII) or other confidential data. This exposure can lead to privacy violations, regulatory compliance issues (e.g., GDPR, HIPAA), and erosion of user trust. Since exploitation requires authenticated access with the 'view-users' role, the threat is limited to insiders or compromised accounts with elevated privileges. The vulnerability does not affect system integrity or availability, so it does not enable data modification or service disruption. However, in environments where Keycloak is used as a central identity provider for critical applications, even limited data leakage can facilitate further social engineering, targeted attacks, or lateral movement. Organizations with large user bases or sensitive user data are at greater risk of reputational damage and legal consequences if this vulnerability is exploited.

To mitigate CVE-2026-3911, organizations should: 1) Review and minimize the assignment of the 'view-users' role to only trusted administrators to reduce the attack surface. 2) Apply the latest patches or updates from Red Hat as soon as they become available, as the vendor will likely release a fix addressing this access control flaw. 3) Implement strict monitoring and auditing of administrative endpoint access, especially those related to user data retrieval, to detect unusual or unauthorized activity. 4) Consider additional access controls or API gateway policies that enforce attribute-level filtering beyond Keycloak's default behavior. 5) Conduct regular security assessments and penetration tests focusing on identity management components to identify similar misconfigurations. 6) Educate administrators on the sensitivity of user attributes and the importance of role-based access control hygiene. 7) If immediate patching is not possible, restrict network access to Keycloak administrative interfaces to trusted management networks or VPNs to limit exposure.