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The Splunk Threat Research Team has uncovered a curious behavior in the Windows utility `Netsh.exe` that can be leveraged to evade detection. This utility processes command-line arguments in a way that allows users to execute firewall commands without fully typing out parameters. Attackers can abuse this feature to bypass security monitoring.
Read the full article here:
You Should Know:
How Attackers Abuse Netsh.exe
`Netsh.exe` (Network Shell) is a legitimate Windows tool for network configuration, but attackers misuse it to:
– Disable firewalls (netsh advfirewall set allprofiles state off)
– Add malicious firewall rules (netsh advfirewall firewall add rule name="EvilRule" dir=in action=allow program="C:\malware.exe")
Evasion Technique
The research highlights that `netsh` allows partial parameter matching, enabling commands like:
netsh advfirewall set allprofiles state off
to be shortened to:
netsh adv set all state off
This obfuscation helps evade string-based detections.
Detection Strategies (Splunk SPL Examples)
To detect such misuse, blue teams can use Splunk queries like:
index=windows EventCode=4688 CommandLine="netshadvfirewallstateoff" | stats count by host, CommandLine
Or for partial commands:
index=windows EventCode=4688 CommandLine="netshadvsetallstateoff" | table _time host CommandLine
Mitigation & Hunting Commands
- Audit Command-Line Logging (Enable in Group Policy):
gpedit.msc → Computer Configuration → Administrative Templates → System → Audit Process Creation → Enable "Include command line in process creation events"
- Monitor Suspicious Netsh Usage (PowerShell):
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4688} | Where-Object {$_.Message -like "netshadvsetstateoff"} - Block Unauthorized Netsh Execution via AppLocker:
<RuleCollection Type="Exe"> <FilePathRule Name="Block Netsh" Action="Deny" Description="Block unauthorized netsh usage" Path="C:\Windows\System32\netsh.exe" /> </RuleCollection>
What Undercode Say
The abuse of `netsh.exe` underscores the importance of monitoring legitimate tools used maliciously. Security teams should:
– Log command-line arguments in Windows Event IDs (4688).
– Use anomaly detection for unusual `netsh` invocations.
– Implement allowlisting via AppLocker or WDAC.
Additional Useful Commands for Blue Teams:
- Check Firewall Status:
netsh advfirewall show allprofiles
- List All Firewall Rules:
netsh advfirewall firewall show rule name=all
- Hunt for Modified Rules (PowerShell):
Get-NetFirewallRule | Where-Object { $_.Modified -gt (Get-Date).AddDays(-1) } - Sysmon Configuration for Netsh Monitoring:
<RuleGroup name="Netsh Monitoring"> <ProcessCreate onmatch="include"> <CommandLine condition="contains">netsh</CommandLine> </ProcessCreate> </RuleGroup>
Expected Output:
A robust detection strategy combining command-line logging, behavioral analysis, and allowlisting can mitigate `netsh.exe` abuse. Security teams should continuously refine detections based on attacker tradecraft.
Reference:
Splunk Threat Research Team – Netsh Evasion
References:
Reported By: Teoderickc Blueteam – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
