olds dynamicmodifiers

naxsi dynamic configuration (aka nginx vars)

Since 0.49, naxsi supports a limited set of boolean variables that can be set to 0 or 1 to override or modify its behaviour.

• naxsi_flag_learning can override Naxsi learning flag.
• naxsi_flag_post_action may be used to disable post_action in learning mode.
• naxsi_flag_enable could override naxsi's SecRulesEnabled.
• naxsi_extensive_log can force naxsi to log the CONTENT of variable matching rules (see notes at bottom).

Gentle reminder

It is important to know that naxsi operates at the REWRITE phase of nginx. Thus, setting those variables directly in the location where Naxsi is present is ineffective (as naxsi will be called before variable set is effective).

This is correct:

 set $naxsi_flag_enable 0;
 location / {
 ...
 }

But this is wrong:

 location / {
          set $naxsi_flag_learning 1;
  ...
 }

With that said, you can use the power of nginx, lua, etc. to change naxsi's behaviour. The presence of these variables will enable/disable learning mode, naxsi itself or force extensive logging. You can thus do things naxsi is usually not able to, like modifying its behaviour according to (nginx) variables set at run-time :

 # Disable naxsi if client ip is 127.0.0.1
 if ($remote_addr = "127.0.0.1") {
  set $naxsi_flag_enable 0;
 }

Those variables can as well be set from lua scripts (see nginx's mod_lua).

naxsi_flag_learning

If the naxsi_flag_learning variable is present, this value will override naxsi's current static configuration regarding learning mode.

 if ($remote_addr = "1.2.3.4") {
 set $naxsi_flag_learning 1;
 }
 location / {
 ...
 }

naxsi_flag_post_action

The post_action option can be used by naxsi to literally forward a request to the DeniedUrl location. It is on by default until naxsi 0.50 (a souvenir from nx_intercept) and is off by default since naxsi 0.51.

naxsi_flag_enable

If the naxsi_flag_enable variable is present and set to 0, naxsi will be disabled in this request. This allows you to partially disable naxsi in specific conditions. To completely disable naxsi for "trusted" users :

 set $naxsi_flag_enable 0;
 location / {
 ...
 }

naxsi_extensive_log

If present and set to 1, this variable will force naxsi to log the CONTENT of variable matching rules. Because of a potential impact on performance, use this with caution. Naxsi will log those to nginx’s error_log, ie:

 NAXSI_EXLOG: ip=%V&server=%V&uri=%V&id=%d&zone=%s&var_name=%V&content=%V