Path Equivalence: 'file.Name' (Internal Dot) leading to Remote Code Execution and/or Information disclosure and/or malicious content added to uploaded files via write enabled Default Servlet in Apache Tomcat.

This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.2, from 10.1.0-M1 through 10.1.34, from 9.0.0.M1 through 9.0.98.

If all of the following were true, a malicious user was able to view security sensitive files and/or inject content into those files:
- writes enabled for the default servlet (disabled by default)
- support for partial PUT (enabled by default)
- a target URL for security sensitive uploads that was a sub-directory of a target URL for public uploads
- attacker knowledge of the names of security sensitive files being uploaded
- the security sensitive files also being uploaded via partial PUT

If all of the following were true, a malicious user was able to perform remote code execution:
- writes enabled for the default servlet (disabled by default)
- support for partial PUT (enabled by default)
- application was using Tomcat's file based session persistence with the default storage location
- application included a library that may be leveraged in a deserialization attack

Users are recommended to upgrade to version 11.0.3, 10.1.35 or 9.0.98, which fixes the issue.

More justification and the patch links are available for all versions here:
[1] https://tomcat.apache.org/security-11.html
[2] https://tomcat.apache.org/security-10.html
[3] https://tomcat.apache.org/security-9.html