New Firewall Rule Added Via Netsh.EXE

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Markus Neis, Sander Wiebing
Source: github.com/SigmaHQ/sigma

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

Known false positives

Legitimate administration activity
Software installations

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1686.003` Disable or Modify System Firewall: Windows Host Firewall

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: New Firewall Rule Added Via Netsh.EXE
id: cd5cfd80-aa5f-44c0-9c20-108c4ae12e3c
status: test
description: Detects the addition of a new rule to the Windows firewall via netsh
references:
    - https://web.archive.org/web/20190508165435/https://www.operationblockbuster.com/wp-content/uploads/2016/02/Operation-Blockbuster-RAT-and-Staging-Report.pdf
author: Markus Neis, Sander Wiebing
date: 2019-01-29
modified: 2023-02-10
tags:
    - attack.defense-impairment
    - attack.t1686.003
    - attack.s0246
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\netsh.exe'
        - OriginalFileName: 'netsh.exe'
    selection_cli:
        CommandLine|contains|all:
            - ' firewall '
            - ' add '
    filter_optional_dropbox:
        CommandLine|contains:
            - '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'
    condition: all of selection_* and not 1 of filter_optional_*
falsepositives:
    - Legitimate administration activity
    - Software installations
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_* and not 1 of filter_optional_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\netsh.exe'
    - OriginalFileName: 'netsh.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains|all:
        - ' firewall '
        - ' add '

Stage 3: `not filter_optional_dropbox`

filter_optional_dropbox:
    CommandLine|contains:
        - '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'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	match	`advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files (x86)\Dropbox\Client\Dropbox.exe" enable=yes profile=Any`	`excludes:CommandLine`
`CommandLine`	match	`advfirewall firewall add rule name=Dropbox dir=in action=allow "program=?:\Program Files\Dropbox\Client\Dropbox.exe" enable=yes profile=Any`	`excludes:CommandLine`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`add` corpus 15 (sigma 13, splunk 1, chronicle 1) `firewall` corpus 3 (sigma 2, splunk 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\netsh.exe` corpus 28 (sigma 28)	`field:"Image" kind:ends_with value:"\netsh.exe"`
`OriginalFileName`	eq	`netsh.exe` corpus 23 (sigma 14, splunk 7, elastic 2)	`field:"OriginalFileName" kind:eq value:"netsh.exe"`

New Firewall Rule Added Via Netsh.EXE

Known false positives

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Stage 3: not filter_optional_dropbox

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Stage 3: `not filter_optional_dropbox`