Security Experts:

Malvertising Campaign Targets Adult Websites to Distribute Ramnit Worm

A new malvertising campaign has been discovered using popular adult websites (each with several million visits per month) to target primarily Canadian and UK visitors. Using pop-under ads, victims were ultimately directed to the RIG exploit kit which sought to drop Ramnit.

Malwarebytes lead malware intelligence analyst Jerome Segura reports that a campaign using the ExoClick ad network sought to infect victims with the Ramnit information-stealing worm. 

An earlier Ramnit botnet was dismantled in a joint operation involving security firms and European police agencies in February 2015; but the malware returned before the end of the year. This was followed by a quiet period until a new version, possibly with a new master, emerged in the summer of 2016.

Pop-under ads are triggered when a user clicks on an item on the site they are visiting. Doing so in this instance launched a pop-under window behind the main page. Redirection from here loaded mostly benign adult portals and offers -- but a 302 redirect also went to a malicious site that performed geolocation fingerprinting before loading the RIG exploit kit.

The danger with malvertising is that it is invisible to the eye and effective from trusted sites. One method of mitigating this threat is to use an ad blocker which prevents all third-party ads, both benign and malicious, from being loaded. Publishers, however, are increasingly detecting such software and not allowing visitors to see the content. This is, strictly speaking, illegal within the European Union, but still happens.

A second defense is to rely on an up-to-date mainstream anti-virus product and hope that it detects the malvertising payload. Segura recommends both. "Ad-blockers are quite effective as a first line of defense to stop malvertising in general," he told SecurityWeek, "while security products will mitigate exploits and malware payload. One solution should not replace the other and they actually complement each other nicely."

Ramnit has evolved into effective banking fraud malware. The geolocation used in this campaign seeks to target Canada and the UK -- two areas that have been repeatedly targeted by Ramnit. "The creators of the Ramnit Trojan (or any banking Trojan for that matter)," explains Segura, "need to have an understanding of each country's financial institutions in order to develop the appropriate tools (webinjects) to capture user information who do online banking. The choice could be motivated simply by the return on investment, likelihood of being detected but also general availability of money mules to transfer funds." Canadian and UK banks are clearly well-understood by the criminals behind the malware.

In this campaign (which has now been blocked by ExoClick), the prime target is individual adults. It would be wrong, however, to assume that malvertising is primarily a consumer threat. Relaxed attitudes to staff using their own devices at work and using the internet to keep up with news makes everyone susceptible. 

"Malvertising isn't just a consumer threat in the sense that any user today is exposed to rogue online adverts, whether it is at home or at work," warns Segura. "Online crooks abuse ad networks to insert malicious redirections into their creative effectively making malvertising a precise and targeted delivery mechanism for malware. Therefore, consumers may be served a different payload than businesses while the distribution via malicious ads remains the same."

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Kevin Townsend is a Senior Contributor at SecurityWeek. He has been writing about high tech issues since before the birth of Microsoft. For the last 15 years he has specialized in information security; and has had many thousands of articles published in dozens of different magazines – from The Times and the Financial Times to current and long-gone computer magazines.