Seamless campaign serves RIG EK via Punycode

The Seamless campaign is one of the most prolific malvertising chains pushing the RIG exploit kit and almost exclusively delivering the Ramnit Trojan. Identification of Seamless is typically easy, due to its use of static strings and an IP literal URLs. However, for over a week now we have been seeing another Seamless campaign running in parallel, making use of special characters.
Rather than using an IP address, this Seamless chain uses a Cyrillic-based domain name, which is transcribed into recognizable characters via Punycode, a visual representation of Unicode. In this blog post, we’ll do a quick historical review of the Seamless gate and describe this latest iteration in a new format.
We noted redirections via adult sites around March 2017 (as pictured below) that were going through a new gate targeting Canada. Due to the presence of the string of the same name in its code, Cisco named this new campaign “Seamless.” Seamless dropped the Ramnit banking Trojan from the very beginning and still continues to do so.

The URL patterns were typically:
These days, web traffic to Seamless still comes from adult portals serving malvertising, eventually redirecting to the same IP literal URLs containing the string test followed by three digits:

Seamless and Punycode
It wasn’t until recent years that domain registrars began to allow for non-English (ASCII) characters in domain names, defined by the Internationalized Domain Names (IDNs) for Applications framework. This allowed for countries to customize services with their own alphabets, which include what we’d otherwise call “special characters,” but have in fact existed long before the Internet was born.
Punycode is a representation of Unicode characters into ASCII used for hostnames, which allows for IDNs, while DNS lookups can still be performed using ASCII characters. The threat actors behind Seamless have been using a domain name containing Cyrillic characters (mostly found in Eastern European countries), which we noticed in our honeypot captures via its Punycode representation.
The call to the Seamless gate was initiated by a malvertising redirection:

It is worth noting that Punycode has been exploited by scammers crafting phishing domain names resembling official brands, as sometimes certain Unicode characters are hard to distinguish from ASCII ones.
It is unclear whether this was a deliberate attempt to bypass intrusion detection systems or if it is simply an odd case similar to previous ones such as the Decimal IP campaign. Time will tell if the Seamless operators maintain it or abandon it in favor of the long-used IP literal URLs.
Indicators of compromise (IOCs)
Note: These IOCs are specific to the Punycode Seamless campaign.
xn--80af6acaaaj9h .xn--p1acf/test441.php
xn--80af6acaaaj9h .xn--p1acf/test551.php
IP address:
The post Seamless campaign serves RIG EK via Punycode appeared first on Malwarebytes Labs.
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