Has anyone written an iRule to filter CVE-2014-6271?

Here is some corrections on your version but the initial version seem more simple and does match all headers so...

when HTTP_REQUEST { 
   foreach header_name [HTTP::header names] {
      foreach header_value [HTTP::header values $header_name] {
           replaced [string match -nocase "() \{*;\};*" $header_value], doesn't match enough
          if { $header_value contains "() \{" } { 
           log local0. "Detected CVE-2014-6271 attack from [IP::client_addr]"
           reject
         }
      }
   }
}

Edit: added a missing ending "*" for the match to work