CVE-2023-42795 is a medium-severity vulnerability classified under CWE-459 (Incomplete Cleanup) affecting multiple versions of Apache Tomcat, a widely used Java servlet container. The issue arises during the recycling of internal objects that Tomcat uses to handle HTTP requests and responses. Specifically, when Tomcat attempts to recycle these objects to improve performance and resource utilization, an error can cause the process to skip certain cleanup steps. This incomplete cleanup leads to residual data from one request or response being inadvertently retained and potentially exposed in subsequent requests handled by the same server instance. Such information leakage can include sensitive data such as authentication tokens, session identifiers, or other private information processed during the HTTP transaction. The vulnerability affects a broad range of Tomcat versions, including long-term support branches (8.5.x and 9.0.x) and newer milestone releases (10.1.x and 11.0.x). Exploitation does not require any privileges or user interaction, and the attack vector is network-based, meaning an attacker can potentially trigger the vulnerability remotely by sending crafted HTTP requests. Although no active exploits have been reported, the nature of the vulnerability makes it a concern for environments where sensitive data is processed. The Apache Software Foundation has addressed the issue in subsequent releases, and upgrading to the patched versions is the primary remediation. The vulnerability does not impact integrity or availability but compromises confidentiality by leaking data across request boundaries.

For European organizations, the incomplete cleanup vulnerability in Apache Tomcat can lead to unauthorized disclosure of sensitive information processed by web applications, including personal data protected under GDPR. This leakage could expose session tokens, user credentials, or other confidential information to attackers, potentially facilitating further attacks such as session hijacking or unauthorized access. Organizations in sectors like finance, healthcare, government, and critical infrastructure that rely heavily on Tomcat for web services are particularly at risk. The breach of confidentiality could result in regulatory penalties, reputational damage, and loss of customer trust. Since the vulnerability does not affect system integrity or availability, the immediate operational impact may be limited, but the data exposure risk is significant. The ease of remote exploitation without authentication increases the threat level, especially in public-facing web applications. European entities with strict data protection requirements must prioritize patching to avoid compliance violations and data breaches.

European organizations should immediately assess their Apache Tomcat deployments to identify affected versions. The primary mitigation is to upgrade to the fixed versions: 8.5.94 or later, 9.0.81 or later, 10.1.14 or later, or 11.0.0-M12 or later. If immediate upgrading is not feasible, organizations should implement strict network controls to limit access to Tomcat servers, such as IP whitelisting and web application firewalls (WAFs) configured to detect anomalous HTTP request patterns. Additionally, review and minimize sensitive data exposure in HTTP responses and ensure session management follows best practices to reduce the impact of potential leaks. Conduct thorough logging and monitoring to detect unusual request patterns that might indicate exploitation attempts. Regularly audit and sanitize application code to avoid storing sensitive data in server-side objects unnecessarily. Finally, maintain an up-to-date inventory of Tomcat instances and enforce patch management policies to prevent similar vulnerabilities from persisting.