A local code execution issue exists in Apache Struts2 when processing malformed XSLT files, which could let a malicious user upload and execute arbitrary files.
Apache Struts versions 2.3 to 2.3.34 and 2.5 to 2.5.16 suffer from possible Remote Code Execution when alwaysSelectFullNamespace is true (either by user or a plugin like Convention Plugin) and then: results are used with no namespace and in same time, its upper package have no or wildcard namespace and similar to results, same possibility when using url tag which doesn't have value and action set and in same time, its upper package have no or wildcard namespace.
The Apache Struts REST Plugin is using XStream library which is vulnerable and allow perform a DoS attack when using a malicious request with specially crafted XML payload. Upgrade to the Apache Struts version 2.5.16 and switch to an optional Jackson XML handler as described here http://struts.apache.org/plugins/rest/#custom-contenttypehandlers. Another option is to implement a custom XML handler based on the Jackson XML handler from the Apache Struts 2.5.16.
In Apache Struts 2.5 to 2.5.14, the REST Plugin is using an outdated JSON-lib library which is vulnerable and allow perform a DoS attack using malicious request with specially crafted JSON payload.
The TextParseUtil.translateVariables method in Apache Struts 2.x before 2.3.20 allows remote attackers to execute arbitrary code via a crafted OGNL expression with ANTLR tooling.
Apache Struts 2.x before 2.3.29 allows remote attackers to execute arbitrary code via a "%{}" sequence in a tag attribute, aka forced double OGNL evaluation. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-0785.
In the Convention plugin in Apache Struts 2.3.x before 2.3.31, and 2.5.x before 2.5.5, it is possible to prepare a special URL which will be used for path traversal and execution of arbitrary code on server side.