[Snort-sigs] Quick uricontent question

Joel Esler jesler at ...435...
Wed Sep 19 17:26:15 EDT 2012

James, in this case %u and such are variable fields.  (The theme is digits and the siteID is also digits if it's the first report)

So, what you'd want is something like this:

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"MALWARE-CNC Win.Trojan.Zeroaccess variant outbound communication"; flow:to_server,established; content:"/counter.img?theme="; nocase; http_uri; content:"&digits="; nocase; http_uri; distance:0; content:"&siteId="; nocase; http_uri; distance:0; pcre:"/theme\=\d+\&digits\=/Ui"; metadata:policy balanced-ips drop, policy security-ips drop, service http; reference:url,www.sophos.com/en-us/why-sophos/our-people/technical-papers/zeroaccess-botnet.aspx; classtype:trojan-activity;)

Now, I haven't tested this against any pcaps or samples, I simply wrote this freehand by looking at the pdf you linked there.

I'll do some testing and we'll try and get this (or something very similar) out.

Joel Esler
Senior Research Engineer, VRT
OpenSource Community Manager

On Sep 19, 2012, at 4:32 PM, James Lay <jlay at ...3266...> wrote:

> So...doing some reading:
> http://www.sophos.com/en-us/why-sophos/our-people/technical-papers/zeroaccess-botnet.aspx
> From the text:
> The first phone home mechanism is through a specially crafted HTTP Get 
> Request that
> takes the following form:
> GET /<unique ID>/counter.img?theme=%u&digits=10&siteId=%u HTTP/1.1\r\n
> Host: <hostname>\r\n
> User-Agent: Opera/9 (Windows NT %u.%u; %s; %s)
> So far here's what I have:
> alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS 
> (msg:"INDICATOR-COMPROMISE ZeroAccess phone home"; 
> content:"User-Agent|3a| Opera/9"; http_header; 
> uricontent:"/counter.img?theme=";
> As I am reading the info on uricontent, the content is already 
> normalized...does that mean I don't have to hex anything with 
> "/counter.img?theme="?  Or does it matter.  Thanks all.
> James
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