CVE-2026-43512

A flaw was found in Apache Tomcat. When DIGEST authentication was configured, any user not known to the configured Realm would be authenticated if they presented the password "null". This allows a remote attacker to bypass security controls.

This Moderate flaw in Apache Tomcat allows an authentication bypass when DIGEST authentication is configured. An attacker can authenticate as any unknown user by providing the password 'null', potentially gaining unauthorized access to applications protected by DIGEST authentication. Red Hat products are only affected if they are configured to use DIGEST authentication, which is not a common, out of the box and expected configuration for Production environments.

Furthermore, because the unknown user is not mapped to any valid realm roles, their access is still restricted by standard application authorization constraints, significantly limiting the actual impact.

The unknown user is not mapped to any existing user, which means, it does not steal credentials nor impersonate an existing user. This new user is expected to have the minimum possible authentication and authorization range within the realm inherited roles.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, disable DIGEST authentication within Apache Tomcat if it is not essential for your environment. This involves modifying the server's authentication configuration to utilize alternative methods or remove the DIGEST realm. A service restart is required for these changes to take effect and may impact functionality relying on DIGEST authentication.