// soc investigation 2026-04-28
SOC321 Windows Defender Evasion Attempt
letsdefend High closed ✓ true positive
mitre/T1110-001 mitre/T1078 mitre/T1059-003 mitre/T1218-011 mitre/T1027 mitre/T1082 mitre/T1049 mitre/T1069 lolbin
analyst verdict TRUE POSITIVE

🎯 MITRE ATT&CK

ID Tactic Technique
T1110.001 Initial Access Brute Force: Password Guessing
T1078 Initial Access Valid Accounts
T1059.001 Execution Command and Scripting Interpreter: PowerShell
T1059.003 Execution Command and Scripting Interpreter: Windows Command Shell
T1218.011 Defense Evasion System Binary Proxy Execution: Rundll32
T1027 Defense Evasion Obfuscated Files or Information
T1082 Discovery System Information Discovery
T1049 Discovery System Network Connections Discovery
T1069 Discovery Permission Groups Discovery

🔎 What

Brute force from 89[.]187[.]177[.]73 (confirmed malicious via AbuseIPDB) succeeded at 07:07 AM with logon event 4624 on account LetsDefend. Attacker conducted hands-on-keyboard recon via cmd spawned from explorer[.]exe including whoami, net user, net share, and PowerShell queries for running services, Defender status, and firewall profile. Attacker ran two LOLBin PoC commands via rundll32 abusing vbscript and mshtml traversal to spawn calc[.]exe. Second variant used LoL45 junk path obfuscation to bypass AV signature matching. First variant caught by AV. No external IPs contacted, no additional payloads executed. Verdict: True Positive - Contained. Machine contained.

🕐 When

Sep 12, 2024 - 07:09 AM

📍 Where

Host Elenora at 172[.]16[.]17[.]126. Brute force from 89[.]187[.]177[.]73. Successful logon at 07:07 AM. Commands executed via cmd and PowerShell spawned from explorer[.]exe.

👤 Who

External threat actor from 89[.]187[.]177[.]73. Gained access via brute force against LetsDefend account. Activity consistent with manual recon and Defender evasion testing - no payload deployment observed.

💡 Why

Attacker enumerated users, network, shares, and security tooling post-access. Rundll32 LOLBin PoC suggests probing Defender detection thresholds. LoL45 obfuscation indicates awareness of known AV signatures for standard mshtml traversal.

📌 IOCs

Type Value Description
IP 89[.]187[.]177[.]73 Attacker IP - brute force source, confirmed malicious AbuseIPDB
IP 172[.]16[.]17[.]126 Host Elenora - compromised endpoint
Account LetsDefend Brute forced account
Process RUNDLL32[.]EXE LOLBin used for Defender evasion PoC

🔬 Analysis Reports

🔗 AbuseIPDB (89[.]187[.]177[.]73) → https://www.abuseipdb.com/check/89.187.177.73?page=5 🔗 LOLBAS - Mshtml → https://lolbas-project.github.io/lolbas/Libraries/Mshtml/