Bypassing Antivirus: What Defendnot Reveals About the Weak Spots in Windows Security

Daily Security Review

In this episode, we dissect one of the most advanced Windows security evasion tools released in recent memory: Defendnot. Designed to exploit undocumented Windows Security Center APIs, this tool disables Windows Defender by impersonating a trusted antivirus and injecting its code into Microsoft-signed Task Manager. We explore how Defendnot bypasses Protected Process Light and security signatures, effectively neutering the built-in antivirus on Windows systems.

The discussion broadens to cover the common antivirus and EDR detection mechanisms — including static analysis, AMSI, ETW, API hooking, IAT inspection, and behavioral monitoring — and the sophisticated techniques attackers now use to bypass them. From DLL injection and reflective loading to direct/indirect syscalls and anti-sandbox checks, we break down the tools and tactics adversaries use to slip past enterprise defenses.

We also discuss the broader implications of tools like Defendnot: how trusted Windows infrastructure is being turned against itself, why these attacks are difficult to mitigate, and what the security community needs to consider moving forward. Whether you're a red teamer, blue teamer, or somewhere in between, this episode is your technical crash course on how modern endpoint protection is being circumvented — and what that means for defenders.