ATT&CK Technique
Regsvcs/Regasm
T1121 · stealth, execution
▤ Generate a SIEM detection for T1121
◈ Deployable detections for T1121
⚠ CVEs mapped to T1121
♛ Hunt package for T1121
Regsvcs and Regasm are Windows command-line utilities that are used to register .NET Component Object Model (COM) assemblies. Both are digitally signed by Microsoft. Adversaries can use Regsvcs and Regasm to proxy execution of code through a trusted Windows utility.
Both utilities may be used to bypass process whitelisting through use of attributes within the binary to specify code that should be run before registration or unregistration: [ComRegisterFunction] or [ComUnregisterFunction] respectively. The code with the registration and unregistration attributes will be executed even if the process is run under insufficient privileges and fails to execute.
Windows
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How to use this page - the detection-engineering loop
Attackers have goals (tactics - “get credentials”, “move laterally”) and techniques are the concrete methods they use to reach them. This page is one method - T1121 - broken into everything you need to catch it.
The loop this page is built for (this is the job):
- Understand the behaviour - read the description and the Atomic Tests to see exactly what the attacker does on a host or network.
- Find the telemetry - what data source would reveal it (process creation, registry, network flow, auth logs). Detection Coverage shows which surfaces already have a rule and which are blind.
- Get or write the detection - adapt ready logic (CAR Analytics, SIEM Detections, Falco, or Sigma via Generate a SIEM detection), or author your own.
- Test it - run an Atomic Test in a lab and confirm your rule actually fires. A detection you have not tested is a hope, not coverage.
- Deploy and tune - push it, then watch for false positives and adjust.
What each panel is for:
Atomic Testssafely reproduce the technique in a lab to validate that a detection fires.
Detection Coveragewhich detection surfaces have a rule for this technique; none is a blind spot to close, or simply not applicable (YARA matches files, not network behaviour).
CAR / SIEM / Falcoready-made detection logic (Splunk SPL, Elastic EQL, Sentinel KQL, Falco) you adapt to your own SIEM.
Mitigationsreduce exposure so the technique is harder to use at all - prevent, not just detect.
Actors / Attributionwho actually uses this, so you prioritise by your own threat model.
Attack Path / LOTLwhat attackers do before and after this step, and the legitimate tools they abuse to do it.
Where this fits: you usually arrive here from a CVE (“which techniques does it enable”) and leave with a tested detection deployed. The buttons above jump straight to building one, the deployable rules, the CVEs that use T1121, and a hunt package.
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Detection Coverage
0/9 layersCoverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma)
none
Analytics (MITRE CAR)
none
Runtime / container (Falco)
none
File / malware (YARA)
none
Network (Suricata/Snort)
none
Vuln scan (Nuclei)
none
SIEM (Splunk ESCU)
none
SIEM (Elastic)
none
SIEM (Azure Sentinel)
none
External lookups - second-class, for what we don’t hold ourselves