Time-of-check Time-of-use (TOCTOU) Race Condition vulnerability during JSP compilation in Apache Tomcat permits an RCE on case insensitive file systems when the default servlet is enabled for write (non-default configuration). This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.1, from 10.1.0-M1 through 10.1.33, from 9.0.0.M1 through 9.0.97.

A flaw was found in Apache Tomcat. In certain conditions and configurations, this vulnerability allows a remote attacker to exploit a path equivalence flaw to view file system contents and add malicious content via a write-enabled Default Servlet in Apache Tomcat. For the vulnerability to be exploited, the following conditions must be true: writes to the default servlet are enabled (disabled by default), sensitive file uploads are sub-directories of a target URL for public uploads, attackers know the names of the files, and those files are subject to partial PUT uploads enabled by default. If an application uses file-based session persistence with default storage and includes exploitable libraries, remote code execution (RCE) is possible.