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.
https://www.darkreading.com/application-security/actively-exploited-bug-struts-2
https://www.securityweek.com/exploitation-of-recent-critical-apache-struts-2-flaw-begins/
https://www.theregister.com/2024/12/17/critical_rce_apache_struts/
https://isc.sans.edu/diary/rss/31520
https://www.theregister.com/2024/12/12/apache_struts_2_vuln/
https://www.openwall.com/lists/oss-security/2023/12/07/1
https://security.netapp.com/advisory/ntap-20231214-0010/
https://lists.apache.org/thread/yh09b3fkf6vz5d6jdgrlvmg60lfwtqhj
http://packetstormsecurity.com/files/176157/Struts-S2-066-File-Upload-Remote-Code-Execution.html