Beginning in March of 2024, Zscaler ThreatLabz observed a threat actor weaponizing a cluster of domains masquerading as legitimate IP scanner software sites to distribute a previously unseen backdoor. The threat actor registered multiple look-alike domains using a typosquatting technique and leveraged GoogleAds to push these domains to the top of search engine results targeting specific search keywords, thereby luring victims to visit these sites.

The newly discovered backdoor uses several techniques such as multiple stages of DLL sideloading, abusing the DNS protocol for communicating with the command-and-control (C2) server, and evading memory forensics security solutions. We named this backdoor “MadMxShell” for its use of DNS MX queries for C2 communication and its very short interval between C2 requests.