Description

A critical security vulnerability in Apache Tomcat, tracked as CVE-2025-24813, is being actively exploited just 30 hours after public disclosure. The flaw affects multiple Tomcat versions, including 11.0.0-M1 to 11.0.2, 10.1.0-M1 to 10.1.34, and 9.0.0-M1 to 9.0.98. It enables remote code execution (RCE) and information disclosure under specific conditions, such as when partial PUT support is enabled and when sensitive files are uploaded to specific subdirectories. Attackers can exploit the flaw to view or inject arbitrary content into sensitive files, and in severe cases, achieve RCE by exploiting Tomcat’s default session persistence mechanism combined with deserialization vulnerabilities. The vulnerability was patched in Tomcat versions 9.0.99, 10.1.35, and 11.0.3. Despite the release of a patch, Wallarm reported that attackers have already started exploiting the flaw using a two-step approach. First, they upload a serialized Java session file via a PUT request, followed by sending a GET request that references the malicious session ID to trigger deserialization and execute malicious payloads. This method abuses Tomcat's file-based session storage and highlights a broader issue with partial PUT handling that allows attackers to upload files and plant backdoors. Given the simplicity of the exploit and the lack of authentication requirements, security experts warn that attackers may soon shift tactics to upload malicious JSP files, modify configurations, and further compromise systems. Organizations using affected versions of Apache Tomcat are strongly advised to update their systems immediately to mitigate the risk of exploitation. Since the flaw is trivial to exploit and attackers can leverage default settings to achieve their objectives, delaying updates poses a significant threat. Security teams should prioritize patching vulnerable instances and enable necessary security controls to protect against unauthorized PUT requests and potential privilege escalation attacks.