Commentary Sophos Security Insights
The Truth About Malvertising
We tend to think of malvertising as short lived, one-oft attacks that somehow managed to momentarily breach the ad network's defenses. The reality is, malvertising is more norm than anomaly and can easily persist on major ad networks for months, even years, at a time.
Malvertising is a consistently pervasive problem, yet it's often treated as an isolated event. A good example of this would be the malicious ads that were served through londonstockexchange.com on the weekend of Feb. 27th. The malicious ads were quickly traced to the unanimis ad provider network and promptly removed from the site. But while that resolved the immediate problem for visitors of londonstockexchange.com for that particular day, the broader problem of this malvertisement run continued. In fact, it has been running without stop since at least September 2010.
This ongoing malvertisement run is not confined to any specific ad network. While unanimis was briefly used around the 27th, the majority of the malicious ads have been delivered via DoubleClick (Google), YieldManager (Yahoo), and rad.msn.com (Microsoft).
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In addition to the traditional ad delivery via websites, the ads are also being pushed through to webmail accounts. Cisco ScanSafe data reveals that just more than 3% of the ads have been delivered via Windows Live (a.k.a. Hotmail) and Yahoo webmail.
In addition to londonstockexchange.com, other popular sites that have delivered the malvertising include:
...and hundreds of others.
The majority of the malware hosts are .co.cc domains, followed by .cz.cc, most commonly using four alphanumeric characters for the domain name. For example:
IP addresses include 126.96.36.199 and 188.8.131.52, hosted by the same offshore provider that hosted the adshufffle attacks in late 2010:
org-name: Offshore Hosting Ltd.
descr: WorkMedia INC.
descr: Offshore Hosting Ltd.
person: George Shetinsky
address: 10, Calea Iesilor str.
For exploit delivery, attackers are using the Black Hole exploit kit, an interesting coincidence given that Black Hole was announced in August 2010 and the malvertisement run began just a few weeks later. One has to wonder whether the author(s) of Black Hole have masterminded the malvertising run to collect stats and showcase (market) the exploit kit.
One of the hallmarks of a successful malvertising run is its ability to deliver the malicious ads selectively so as to avoid notice. One way to do this is to use cloaking, only serving the ads during specific times in specific geographical regions and only if the visitor meets some predetermined criteria. Looking at the User Agents, we find the following breakdown among those encountering the malicious ads:
USERAGENT - %
Java (JVM/JRE) - 56%
Firefox - 4%
Safari - 3%
MSIE 7.0 - 17%
MSIE 8.0 - 13%
MSIE 6.0 - 6%
Other - 1%
This particular ongoing malvertising run makes up less than 1% of Web malware for the period (September 2010 through current day). This low and steady pace is likely a chief reason the attacks have continued to run for such an extended period of time. It also underscores the ability of attackers to not only deliver malvertising via all of the major ad networks, but to do so for an extended period of time with few repercussions.
Of course, part of the reason for the successful run can be tracked to the inability of some traditional scanners to detect the malicious ads. Fifteen percent of the malvertisements blocked by Cisco ScanSafe were not detectable via traditional signature scanners at time of encounter. (These were instead blocked by ScanSafe Outbreak Intelligence.)
Sixty-three percent of the exploits delivered were Java-based; only 5% were malicious PDFs exploiting vulnerabilities in Adobe Reader and A -- - if not most -- exploit kits have been favoring Java exploits since the first quarter of 2010. Of course, other exploits are also being rendered. A sampling of observed exploits include:
Successful delivery and exploit leads to the silent installation of scareware (a.k.a. rogue AV) and a downloader trojan. The downloader attempts to install additional malware from a secondary set of domains that are constantly swapped out. Recent examples include berdfina.com, acholer.com, and carsero.com, all hosted at 212.134.133.* IP addresses. The secondary download domains also use Black Hole.
The key takeaway isn't the successful run via these Black Hole rendered malvertisements, but rather that this is just one of many long-term, successful malvertising runs slipping through major ad networks on a continued, prolonged basis. It's like cockroaches. For every site that makes headlines for a malicious ad run, there are hundreds -- even thousands -- that are operating just below most people's radar.
Mary Landesman is an antivirus professional and senior security researcher for ScanSafe, now part of Cisco. In 2009 she was awarded a Microsoft MVP for her work in consumer security.