CVE-2024-56337 is a critical vulnerability classified as a Time-of-check Time-of-use (TOCTOU) race condition in the Apache Tomcat server, a widely used Java-based web server and servlet container. This flaw affects multiple Tomcat versions: from 11.0.0-M1 through 11.0.1, 10.1.0-M1 through 10.1.33, 9.0.0.M1 through 9.0.97, and older EOL versions including 8.5.0 through 8.5.100. The vulnerability stems from the interaction between Tomcat's default servlet write capability and the behavior of the Java system property sun.io.useCanonCaches, which controls caching of canonical file paths. On case-insensitive file systems (such as Windows NTFS or macOS APFS), if the default servlet is configured with write enabled (readonly initialization parameter set to false, which is non-default), and the sun.io.useCanonCaches property is not properly set, a race condition can occur during file access checks. This TOCTOU race condition allows an attacker to exploit the timing gap between the file existence check and its subsequent use, potentially leading to unauthorized file manipulation, arbitrary code execution, or denial of service. The mitigation for a related vulnerability CVE-2024-50379 was incomplete, necessitating additional configuration. Specifically, users running Tomcat on Java 8 or Java 11 must explicitly set sun.io.useCanonCaches=false (it defaults to true), while on Java 17 it must be set to false if configured (default is false). Java 21 and later have removed this problematic cache, requiring no further action. Tomcat versions 11.0.3, 10.1.35, and 9.0.99 and later include built-in checks to enforce correct sun.io.useCanonCaches settings and will set it to false by default where possible. The CVSS v3.1 score is 9.8 (critical), reflecting the vulnerability's network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability. No known exploits are currently reported in the wild, but the severity and ease of exploitation warrant urgent attention.

For European organizations, the impact of CVE-2024-56337 is significant due to the widespread use of Apache Tomcat in enterprise web applications, government portals, and critical infrastructure services. Exploitation could allow attackers to bypass file access controls, modify or replace files, execute arbitrary code, or cause service outages, leading to data breaches, service disruption, and loss of trust. Organizations running Tomcat on Windows or macOS servers are particularly vulnerable due to the case-insensitive file system requirement. The vulnerability affects confidentiality (unauthorized data access), integrity (file tampering), and availability (denial of service). Given the criticality and network exposure, attackers could remotely exploit this flaw without authentication or user interaction, increasing the risk of widespread compromise. This threat is especially concerning for sectors such as finance, healthcare, government, and telecommunications, where Tomcat-based applications are common and data sensitivity is high. Failure to mitigate promptly could result in regulatory penalties under GDPR due to data breaches.

European organizations should take the following specific steps to mitigate CVE-2024-56337: 1) Immediately identify all Apache Tomcat instances running versions affected by this vulnerability, including EOL versions still in use. 2) Upgrade Tomcat to versions 9.0.99, 10.1.35, or 11.0.3 or later, which include built-in mitigations and enforce correct configuration. 3) For environments where upgrading is not immediately feasible, explicitly set the Java system property sun.io.useCanonCaches=false on Java 8 and Java 11 to disable the problematic canonical path caching. 4) Verify that the default servlet's readonly initialization parameter is set to true (write disabled) unless write access is strictly required and properly secured. 5) Prefer running Tomcat on case-sensitive file systems (e.g., Linux ext4) to avoid the underlying race condition scenario. 6) Conduct thorough testing of web applications after configuration changes to ensure no functionality is broken. 7) Monitor logs and network traffic for suspicious activity indicative of exploitation attempts. 8) Implement strict access controls and network segmentation to limit exposure of Tomcat servers. 9) Maintain an inventory of Java runtime versions in use and plan upgrades to Java 21 or later, where this issue is resolved at the JVM level. 10) Educate DevOps and security teams about this vulnerability and ensure patch management processes prioritize this critical issue.