New Firewall Rule Added Via Netsh.EXE

Severity: medium
Author: Markus Neis, Sander Wiebing
Source: upstream

Detects the addition of a new rule to the Windows firewall via netsh

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1562.004` Impair Defenses: Disable or Modify System Firewall

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\netsh.exe'
OriginalFileName: netsh.exe

Stage 2: `all of selection_cli`

CommandLine|contains: ' add '
CommandLine|contains: ' firewall '

Stage 3: `not 1 of filter_optional_dropbox`

or:
CommandLine|contains: 'advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files (x86)\Dropbox\Client\Dropbox.exe" enable=yes profile=Any'
CommandLine|contains: 'advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files\Dropbox\Client\Dropbox.exe" enable=yes profile=Any'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`add` corpus 11 (sigma 11) `firewall` corpus 2 (sigma 2) `advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files (x86)\Dropbox\Client\Dropbox.exe" enable=yes profile=Any` `advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files\Dropbox\Client\Dropbox.exe" enable=yes profile=Any`
`Image`	ends_with	`\netsh.exe` corpus 16 (sigma 16)
`OriginalFileName`	eq	`netsh.exe` corpus 14 (sigma 14)