[Oisf-users] HTTP missing user agent detection

Francis Trudeau ftrudeau at emergingthreats.net
Sat Nov 1 15:39:34 UTC 2014

I don't think there's a specific dedicated way to test for this, but
this should work:

content:!"User-Agent|3a 20|"; http_header;

Probably could get a little tricky with pcre to make it doesn't FP on
something else in the header, but I wouldn't think that would be


On Thu, Oct 30, 2014 at 4:21 AM, Evrard, Benjamin
<benjamin.evrard at adelpha.be> wrote:
> Hi everyone !
> I've been trying to find if it's possible to write a rule that's
> triggered when specific fields are completely absent from a request or
> empty.
> In this specific case, I'd like to trigger an alert when no user agent
> is sent with an HTTP request.
> I have found rulesets achieving the same kind of match I try to
> (https://github.com/decanio/suricata/blob/master/rules/http-events.rules)
> but could see no trace of a way to specifically match the absence of
> user-agent. I also looked at the source code of the app-layer-htp
> module (https://github.com/inliniac/suricata/blob/master/src/app-layer-htp.c)
> but could not find any lead there either.
> Does this feature exist somewhere else or is it planned to be included
> in some future release ?
> Best regards,
> Evrard B.
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