How to fix apache struts2 s2-045 vulnerable with f5 irule ?

The Vulnerability has to do with File upload so, no use checking every single request.

This is why my iRule on codeshare inspects the Content-Type for POST requests only.

Here.

    when HTTP_REQUEST {
      if { [HTTP::method] equals "POST" } {

            if { not ( [HTTP::header Content-Type] equals "multipart/form-data" or [HTTP::header Content-Type] equals "application/x-www-form-urlencoded" or [HTTP::header Content-Type] equals "text/plain" ) } {
                reject
                log local0. "Rejecting a POST request with Content-type [HTTP::header Content-Type]  to  [HTTP::uri]  from  [IP::client_addr]"
            }
      }
}  

One could restrict this further by matching against the URL(s) which present the upload form:

when HTTP_REQUEST {
      if { [HTTP::uri] equals "" } {

            if { not ( [HTTP::header Content-Type] equals "multipart/form-data" or [HTTP::header Content-Type] equals "application/x-www-form-urlencoded" or [HTTP::header Content-Type] equals "text/plain" ) } {
                reject
                log local0. "Rejecting a POST request with Content-type [HTTP::header Content-Type]  to  [HTTP::uri]  from  [IP::client_addr]"
            }
      }
}