Rule name: "Skopnix: CVE-2016-3081 exploitation attempt"
Rule type: Event
Test stack:
  - and when the event(s) were detected by one or more of [your web server / WAF / proxy log sources]
  - and when the event matches this AQL filter query: ("URL" ILIKE '%/index.action%' AND "URL" ILIKE '%method:%23_memberAccess%3d@ognl.OgnlContext@DEFAULT_MEMBER_ACCESS,%23res%3d%40org.apache.struts2.ServletActionContext%40getResponse(),%23res.setCharacterEncoding(%23parameters.encoding%5B0%5D),%23w%3d%23res.getWriter(),%23s%3dnew+java.util.Scanner(@java.lang.Runtime@getRuntime().exec(%23parameters.cmd%5B0%5D).getInputStream()).useDelimiter(%23parameters.pp%5B0%5D),%23str%3d%23s.hasNext()%3f%23s.next()%3a%23parameters.ppp%5B0%5D,%23w.print(%23str),%23w.close(),1?%23xx:%23request.toString%')
Response: dispatch new event / create offense indexed by Destination IP (the targeted server); annotate "Skopnix CVE-2016-3081 attempt".
FP-safety: correlate with the HTTP status / response size; scanner noise is an attempt, not a breach.