CVE-2024-21733 is a vulnerability in the Apache Tomcat web server software, specifically affecting versions 8.5.7 through 8.5.63 and 9.0.0-M11 through 9.0.43. The issue is categorized under CWE-209, which pertains to the generation of error messages containing sensitive information. When an error occurs, the server may inadvertently include details that could reveal internal system information, such as configuration data, file paths, or other sensitive runtime information. This leakage occurs without requiring any authentication or user interaction, making it remotely exploitable by an attacker who can send crafted requests to the affected Tomcat server. The vulnerability does not impact integrity or availability but compromises confidentiality by exposing potentially exploitable information. The Apache Software Foundation has addressed this issue in versions 8.5.64 and 9.0.44 onwards. No public exploits have been reported yet, but the presence of sensitive information in error messages can facilitate reconnaissance and subsequent targeted attacks. The vulnerability is scored 5.3 on the CVSS v3.1 scale, reflecting a medium severity level with network attack vector, low complexity, no privileges required, and no user interaction needed. Organizations running affected Tomcat versions should prioritize upgrading to the patched releases and review their error handling and logging configurations to minimize sensitive data exposure.

For European organizations, the primary impact of CVE-2024-21733 is the unintended disclosure of sensitive information through error messages generated by Apache Tomcat servers. This information leakage can aid attackers in mapping the internal environment, identifying software versions, file structures, or configuration details, which can be leveraged to craft more effective attacks such as privilege escalation, code injection, or lateral movement. While the vulnerability does not directly allow code execution or denial of service, the confidentiality breach can compromise sensitive business data or intellectual property. Organizations in sectors such as finance, government, healthcare, and critical infrastructure that rely heavily on Apache Tomcat for web applications are particularly at risk. The ease of remote exploitation without authentication increases the threat surface. Additionally, the exposure of sensitive information may violate data protection regulations like GDPR if personal or sensitive data is leaked, potentially leading to compliance issues and reputational damage.

1. Upgrade Apache Tomcat to version 8.5.64 or 9.0.44 or later immediately to apply the official fix for this vulnerability. 2. Review and harden error handling configurations to ensure that error messages do not reveal sensitive internal information; consider customizing error pages to display generic messages. 3. Implement web application firewalls (WAFs) with rules to detect and block suspicious requests that may trigger error conditions. 4. Conduct regular security audits and penetration testing focusing on error message disclosures and information leakage. 5. Monitor server logs for unusual access patterns or repeated error generation attempts that could indicate exploitation attempts. 6. Limit exposure of Tomcat management and administrative interfaces to trusted networks only. 7. Educate development and operations teams about secure coding and error handling best practices to prevent similar issues. 8. If upgrading immediately is not feasible, consider temporary mitigations such as disabling detailed error reporting or using reverse proxies to filter error responses.