A recently disclosed security flaw in Apache Tomcat, tracked as CVE-2025-24813, is already being actively exploited in the wild. This vulnerability affects several versions of Tomcat, including 9.0.0-M1 to 9.0.98, 10.1.0-M1 to 10.1.34, and 11.0.0-M1 to 11.0.2. The issue stems from improper handling of certain configurations, such as enabling partial PUT support and using file-based session persistence. Under these conditions, the flaw allows remote code execution or information disclosure, which could expose sensitive data or allow attackers to inject arbitrary content into security-sensitive files.
Exploitation of the flaw is carried out by sending a PUT request containing a Base64-encoded Java payload, which is then uploaded to Tomcat’s session storage directory.
Once the payload is uploaded, an attacker sends a GET request containing the malicious session ID. This triggers Tomcat to deserialize and execute the malicious Java code, granting attackers full control over the affected server. This method of exploitation is alarmingly simple and does not require authentication, making it easy for attackers to carry out the attack on vulnerable systems.
The vulnerability has already seen exploitation attempts, and exploit code was published on a Chinese forum shortly after the flaw was discovered. Wallarm, a cybersecurity firm, noted that the exploit’s ease of execution, combined with the lack of authentication requirements, makes this vulnerability especially dangerous. Attackers only need to ensure that Tomcat uses file-based session storage, a common configuration in many deployments. Furthermore, the exploit bypasses traditional security filters through Base64 encoding, making it difficult to detect and mitigate.
To mitigate the risk, the Apache Foundation released security patches in versions 9.0.99, 10.1.35, and 11.0.3. Users of affected versions are urged to upgrade immediately.
Alternatively, users can configure Tomcat to disable partial PUT support or avoid storing security-sensitive files in subdirectories of public upload paths. Wallarm also raised concerns that this vulnerability could lead to even more severe remote code execution (RCE) vulnerabilities, especially if attackers begin uploading malicious JSP files or modifying configurations outside of session storage. This may only be the first wave of attacks stemming from this flaw.
