CrowdStrike Researchers Investigate the Threat of Patchless AMSI Bypass Attacks

This report explains a stealthy, patchless AMSI evasion technique where attackers place hardware breakpoints on target function addresses and use a Vectored Exception Handler to catch EXCEPTION_SINGLE_STEP events, modify the thread CONTEXT (e.g., RIP) and alter execution flow without changing memory contents—reducing detection from integrity checks. It highlights the use of DR0–DR3 debug registers and how these mechanisms enable silent hooking and anti-analysis behaviors in malware.