Malware analysts: this reverse engineering is absolutely worth your time. Red teamers: you don't need to bring a vulnerable driver. Detection engineers: your trusted-driver assumptions just got awkward. A security researcher (@vinopaljiri) reversed Microsoft Defender's BTR.sys across 18 signed builds, found the same hard-coded encryption key, then built BTR_CLI to feed valid transactions into Defender's own Microsoft-signed Ring 0 remediation driver. The result: kernel-level file + registry operations and a demonstrated path to disarm security tooling. No memory corruption. No classic BYOVD. No CVE. No patch coming. The defensive technology became the offensive primitive. Research by @vinopaljiri / @_CPResearch_ : research.checkpoint.com/2026… #RedTeam #DetectionEngineering #MalwareAnalysis