Multi-payload Gootloader platform stealthily delivers malware and ransomware

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The delivery method for the six-year-old Gootkit financial malware has been developed into a complex and stealthy delivery system for a wide range of malware, including ransomware. Sophos researchers have named the platform Gootloader. It is actively delivering malicious payloads through tightly targeted operations in the US, Germany and South Korea. Previous campaigns also targeted internet users in France.

Gootloader

The Gootloader infection chain begins with sophisticated social engineering techniques that involve hacked websites, malicious downloads, and manipulated search engine optimization (SEO). When someone types a question into a search engine such as Google, the hacked websites appear among the top results.

To ensure targets from the right geographies are captured, the adversaries rewrite website code “on the go” so that website visitors who fall outside the desired countries are shown benign web content, while those from the right location are shown a page featuring a fake discussion forum on the topic they’ve queried. The fake websites are visually identical regardless of whether they are in English, German or Korean.

The fake discussion forum includes a post from a “site administrator,” with a link to a download. The download is a malicious Javascript file that initiates the next stage of compromise.

From this point on, the attack proceeds covertly, using a wide range of complicated evasion techniques, multiple layers of obfuscation, and fileless malware that is injected into memory or the registry where conventional security scans cannot reach it. Gootloader is currently delivering Kronos financial malware in Germany, and the post-exploitation tool, Cobalt Strike, in the US and South Korea. It has also delivered REvil ransomware and the Gootkit trojan itself.

“The developers behind Gootkit appear to have shifted resources and energy from delivering just their own financial malware to creating a stealthy, complex delivery platform for all kinds of payloads, including REvil ransomware,” said Gabor Szappanos, threat research director at Sophos. “This shows that criminals tend to reuse their proven solutions instead of developing new delivery…

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