Spam campaigns leveraging .tk domains
For the last couple quarters, the Zscaler ThreatLabZ research team has been closely monitoring services that provide free domain names. We’ve identified a campaign utilizing '.tk' TLD (top level domain) domains that starts with compromised sites as the initial vector to redirect users to either fake blog sites to generate ad revenue or fake tech support sites that claim to remove viruses.
Based on our analysis of this campaign data till now, we are estimating at least 20K+ USD per month in revenue being generated from Ad Fraud activities alone. In this blog, we will share our analysis of this campaign.
During July, we saw activity from many compromised sites, as shown in the graph below.
Fig 1: DotTk campaign hits of July 2018
Some of the compromised sites have plain-text injected redirection code, as shown in the below image.
Fig 2: Sites showing plain-text injected redirection code
Many sites have packed and obfuscated injected redirection code, as shown in below image.
Fig 3: Obfuscated injected redirection code
After decoding, the script appears as follows:
Fig 4: Deobfuscated injected redirection code
The redirection code shown in the above image redirects to the .tk campaign.
Fig 5: Redirection to .tk campaign
The third technique used in compromised sites for hiding injected code is shown in the below image.
Fig 6: Hiding injected redirection code
The encrypted script in the above image is shown, decrypted, below:
Fig 7: Decrypted redirection code
In this case, it is not redirecting for every hit; instead, redirection takes place when a random number 3 appears, and the redirected site again redirects to the .tk domains.
We have found 3,804 unique .tk domains since May 2018, which are included in this campaign.
You can find the .tk campaign URLs here.
Fake blogger site redirections:
In this case, the .tk campaign URL redirects to a fake blogging site for the sole purpose of showing ads:
vertdfgsderawee[.]tk/index/?2101505838590 redirects to frenkulok[.]info/latest
Fig 8: Fake blogging site redirect
The redirection URL at vertdfgsderawee[.]tk/index/?2101505838590 changes each time, so the redirect shown here, frenkulok[.]info/latest, will be different on another visit.
This URL redirects to the "latest" blogging content, as shown in the below image.
Fig 8: The "latest" blogging site redirect
The .tk campaign redirects to one of the below 72 fake blogging content sites.
The IP address associated to all these websites is the same - 162.244.35[.]55
The website traffic and Alexa rank of these sites are increasing daily.
Fig 9: Website traffic and Alexa rank of fake blogging sites
The daily and monthly revenue estimates of one of the sites is shown below.
Fig 10: Estimated monthly ad revenues from one fake blogging site
If we consider that the average monthly advertising revenue from one website is $300, we can extrapolate that for 72 domains, the monthly revenue could be as high as $21,600.
Fake tech support redirection:
In this case, the .tk campaign URL redirects to a fake tech support website and displays fake alert messages that ask users to call a given number for technical assistance.
Fig 10: Fake tech support website redirect
Redirected tech support scam site:
Fig 11: Redirected tech support scam site
Below are the tech support scam URLs that are appearing after redirection from the .tk campaign.
The scam campaign involving .tk domains has been active since at least May 2018. Over the last three months, this campaign has largely been redirecting users to fake blogger sites and tech support scam sites, but it's reasonable to assume that in the future, the campaign may start redirecting to phishing sites, exploit kit gates, or any malicious site that can generate revenue in one way or another.