An attacker can manipulate file upload params to enable paths traversal and under some circumstances this can lead to uploading a malicious file which can be used to perform Remote Code Execution. Users are recommended to upgrade to versions Struts 2.5.33 or Struts 6.3.0.2 or greater to fix this issue.
Apache Struts Showcase App 2.0.0 through 2.3.13, as used in Struts 2 before 2.3.14.3, allows remote attackers to execute arbitrary OGNL code via a crafted parameter name that is not properly handled when invoking a redirect.