VirtualAllocEx is a Windows API that reserves or commits memory in another process. Instead of allocating memory only in the current program, it targets a remote process handle, which makes it useful for interprocess tasks and also attractive to attackers. In practice, it is often part of a code-injection chain: a process allocates space in a target, writes payload data there, and then arranges for that code to execute.
This matters because security tools frequently watch for remote memory allocation as a sign of process injection. A call to VirtualAllocEx is not automatically malicious, but it becomes suspicious when it comes from an unexpected parent-child pair, is followed by remote writes or thread creation, or is paired with unusual memory protection changes. Defenders use this signal for EDR detections, baselining, and incident triage, while attackers may try to avoid it by using alternate delivery paths that blend into normal Windows behavior.