ModSecurity and custom headers

[Andrei <lagged@xxxxxxxxx>]

Hi all,

How can I add a custom header using the 'msg' value from a ModSecurity rule, for all rules triggered? I'm basically trying to track the ModSec block reason at an edge point (Varnish) based on Apache's response.

For example, I would like:

SecRule REQUEST_URI "/modsectest" "log,deny,status:406,phase:1,t:none,id:9084310,msg:'ModSec Log Test'"

To add a 'X-ModSec-Block' response header with the value 'ModSec Log Test' in this case. I understand this might be better suited with setenv + mod_headers due to blocks being done at different phases, and found http://serverfault.com/questions/796088/modsecurity-creating-a-new-request-header-from-secrule which seems similar to this scenario, just that it's not quite working out for me. Any help is greatly appreciated!

Andrei