It is quite common for Chinese-speaking threat actors to share tools and methodologies: one such example is the infamous “DLL side-loading triad”: a legitimate executable, a malicious DLL to be side-loaded by it and an encoded payload, generally dropped from a self-extracting archive. This was first thought to be a signature of LuckyMouse, but we have observed other groups using similar “triads”, including HoneyMyte. While it is not possible to attribute attacks based on this technique alone, efficient detection of such triads reveals more and more malicious activity.
We recently described one such file, called “FoundCore”, which caught our attention because of the various improvements it brought to this well-known infection vector. We discovered the malware as part of an attack against a high-profile organization in Vietnam. From a high-level perspective, the infection chain follows the expected execution flow: