High CPU

Following are some of the functionality and high CPU related debugging issues encoutered and the best practices to follow when working with Web App Firewall:

Check Policy hits, Bindings, Network configuration, Web App Firewall configuration

  • Identify misconfiguration

  • Identify vserver that is serving the affected traffic

Inspect logs in the following log files for security violations and recent configuration changes

  • /var/log/ns.log

  • /var/nslog/import.log

  • /var/nslog/aslearn.log

  • tail -f /var/log/ns.log | grep APPFW_SIGNATURE_MATCH


Jun 13 01:11:09 <> CEF:0|Citrix|NetScaler|NS11.0|APPFW| APPFW_SIGNATURE_MATCH|6|src= spt=61141 method=GET request= msg=Signature violation rule ID 807: web-cgi /wwwboard/passwd.txt access cn1=140 cn2=841 cs1=pr_ffc cs2=PPE0 cs3=OyTgjbXBqcpBFeENKDlde3OkMQ00001 cs4=ALERT cs5=2015 cs6=web-cgi act=not blocked

Isolate the traffic that is effected

  • Isolate the profile

  • Isolate the security check

  • Isolate the URL, vserver and traffic parameters

Conditional profile level trace helps identify the traffic and violation records

  • set appfw profile <profile> -trace ON
  • start nstrace -mode APPFW -size 0
  • stop nstrace

Note: Ensure that the trace is collected with -size 0 option.

Check appfw, dht, IP reputation activity counters

  • nsconmsg -g as_ -g appfwreq_ -g iprep -d current

Monitor window size for resets in connection

  • Appfw sets the window size to 9845 when Citrix ADC resets the connection due to an invalid http message.


  • Malformed request received - connection reset
  • High CPU related issues
  • Check data sheets for system limits
  • Inspect for cpu usage, appfw, DHT and memory related activity. Monitor appfw sessions
  • nsconmsg -g cc_cpu_use -g appfwreq -g as -g dht -g mem_AS_OBJ -g mem_AS_COMPONENT -d current

• Monitor memory allocated and freed from Web App Firewall components and objects during the target time period.  It helps in isolating the protection leading to high CPU usage.

     - Profiler output

     - Observe logs

 •  Isolate appfw check leading to high CPU

      - startURLClosure

      - Formfiledconsistency

      - CSRF

      - Cookie protections

      - Referer header check

Ascertain that autoupdate of signatures is not leading to high CPU (Disable to confirm).

High CPU