Detect Disable or Modify System Firewall in CrowdStrike LogScale
Adversaries may disable or modify system firewalls in order to bypass controls limiting network usage. Changes could be disabling the entire mechanism as well as adding, deleting, or modifying particular rules. This can be done via command-line tools (netsh, iptables, ufw, pfctl), editing Windows Registry keys, or through the Windows Control Panel. On ESXi, firewall rules may be modified via esxcli. Adversaries may add new firewall rules for RDP on non-standard ports or open all traffic to enable C2, lateral movement, and data exfiltration.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1562 Impair Defenses
- Sub-technique
- T1562.004 Disable or Modify System Firewall
- Canonical reference
- https://attack.mitre.org/techniques/T1562/004/
LogScale Detection Query
#event_simpleName=ProcessRollup2
| CommandLine = /(?i)(netsh\s+advfirewall\s+set|netsh\s+advfirewall\s+firewall\s+(add|delete)|netsh\s+firewall\s+set\s+opmode\s+disable|Set-NetFirewallProfile.{0,60}Enabled.{0,10}False|(New|Remove)-NetFirewallRule|iptables\s+(-F|-X|-P\s+(INPUT|FORWARD)\s+ACCEPT)|ufw\s+disable|pfctl\s+-d|esxcli\s+network\s+firewall\s+set)/
| FirewallAction := if(
CommandLine = /(?i)(state off|opmode disable|Enabled.*False|ufw disable|pfctl -d)/, "Firewall Disabled",
CommandLine = /(?i)(firewall add|New-NetFirewallRule)/, "Rule Added",
CommandLine = /(?i)(firewall delete|Remove-NetFirewallRule)/, "Rule Deleted",
CommandLine = /(?i)iptables -[FX]/, "IPTables Flushed",
CommandLine = /(?i)iptables -P.*ACCEPT/, "IPTables Policy ACCEPT",
"Other Modification"
)
| table([@timestamp, ComputerName, UserName, FileName, CommandLine, FirewallAction, ParentBaseFileName, ParentCommandLine])
| sort(@timestamp, order=desc)Detects firewall disablement or modification events via CrowdStrike Falcon's ProcessRollup2 telemetry by matching command-line arguments of processes invoking netsh, PowerShell firewall cmdlets, iptables, ufw, pfctl, or esxcli. Categorizes the firewall action for analyst prioritization.
Data Sources
Required Tables
False Positives & Tuning
- Authorized IT operations team members running firewall configuration scripts as part of documented change management processes, particularly on server build pipelines.
- CrowdStrike Falcon sensor itself or other endpoint security agents modifying host firewall rules as part of their normal operation and self-protection mechanisms.
- Software deployment systems (SCCM, Intune, Chef, Ansible) configuring host firewall rules during application installation or OS baseline hardening.
Other platforms for T1562.004
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Disable Windows Firewall All Profiles
Expected signal: Sysmon Event ID 1: netsh.exe process creation. Windows Firewall Event ID 2003: Firewall profile changed. Each profile state change generates a separate event.
- Test 2Add Firewall Rule for RDP on Non-Standard Port
Expected signal: Sysmon Event ID 1: netsh.exe with 'firewall add rule'. Windows Firewall Event ID 2004: A rule has been added.
- Test 3Flush IPTables Rules on Linux
Expected signal: Auditd execve syscall records for iptables. Syslog entries for iptables commands. MDE DeviceProcessEvents if MDE for Linux is deployed.
References (4)
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