Heap-based AMSI bypass for MS Excel VBA and others

This blog post describes how to bypass Microsoft's AMSI (Antimalware Scan Interface) in Excel using VBA (Visual Basic for Applications). In contrast to other bypasses this approach does not use hardcoded offsets or opcodes but identifies crucial data on the heap and modifies it. The idea of an heap-based bypass has been mentioned by other researchers before but at the time of writing this article no public PoC was available. This blog post will provide the reader with some insights into the AMSI implementation and a generic way to bypass it.