Malicious Defender Tampering via UnDefend Aggressive Flag

ATT&CK techniques

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects execution of the UnDefend tool undef.exe with its -agressive flag, an EDR-tampering utility seen in a Huntress-investigated Nightmare-Eclipse intrusion that targeted the mpavbase.vdm Defender signature file. The distinctive misspelled flag identifies the specific tool used to disable endpoint protection. Disabling security controls precedes credential theft and lateral movement.

Reporting behind it

Related detections9 linkedT1685 — drag to rearrange

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Malicious Defender Tampering via UnDefend Aggressive Flag

Pivot detection · T1685 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

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