Outbound Network Connection Initiated By Script Interpreter

Status: test
Severity: high
Log source: category network_connection, product windows
Author: frack113, Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects a script interpreter wscript/cscript opening a network connection to a non-local network. Adversaries may use script to download malicious payloads.

Known false positives

Legitimate scripts

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1105` Ingress Tool Transfer

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 3: Network connection

Rule body

title: Outbound Network Connection Initiated By Script Interpreter
id: 992a6cae-db6a-43c8-9cec-76d7195c96fc
related:
    - id: 08249dc0-a28d-4555-8ba5-9255a198e08c
      type: derived
status: test
description: Detects a script interpreter wscript/cscript opening a network connection to a non-local network. Adversaries may use script to download malicious payloads.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/28d190330fe44de6ff4767fc400cc10fa7cd6540/atomics/T1105/T1105.md
author: frack113, Florian Roth (Nextron Systems)
date: 2022-08-28
modified: 2024-03-13
tags:
    - attack.command-and-control
    - attack.t1105
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Initiated: 'true'
        Image|endswith:
            - '\wscript.exe'
            - '\cscript.exe'
    filter_main_local_ranges:
        DestinationIp|cidr:
            - '127.0.0.0/8'
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '169.254.0.0/16'
            - '::1/128'  # IPv6 loopback
            - 'fe80::/10'  # IPv6 link-local addresses
            - 'fc00::/7'  # IPv6 private addresses
    filter_main_ms_ranges:
        DestinationIp|cidr: '20.0.0.0/11' # Microsoft range, caused some FPs
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Legitimate scripts
level: high

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    Initiated: 'true'
    Image|endswith:
        - '\wscript.exe'
        - '\cscript.exe'

Stage 2: `not filter_main_*`

filter_main_local_ranges:
    DestinationIp|cidr:
        - '127.0.0.0/8'
        - '10.0.0.0/8'
        - '172.16.0.0/12'
        - '192.168.0.0/16'
        - '169.254.0.0/16'
        - '::1/128'
        - 'fe80::/10'
        - 'fc00::/7'
filter_main_ms_ranges:
    DestinationIp|cidr: '20.0.0.0/11'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`DestinationIp`	cidr_match	`10.0.0.0/8`	`excludes:DestinationIp` `field:"DestinationIp" value:"10.0.0.0/8"`
`DestinationIp`	cidr_match	`127.0.0.0/8`	`excludes:DestinationIp` `field:"DestinationIp" value:"127.0.0.0/8"`
`DestinationIp`	cidr_match	`169.254.0.0/16`	`excludes:DestinationIp` `field:"DestinationIp" value:"169.254.0.0/16"`
`DestinationIp`	cidr_match	`172.16.0.0/12`	`excludes:DestinationIp` `field:"DestinationIp" value:"172.16.0.0/12"`
`DestinationIp`	cidr_match	`192.168.0.0/16`	`excludes:DestinationIp` `field:"DestinationIp" value:"192.168.0.0/16"`
`DestinationIp`	cidr_match	`20.0.0.0/11`	`excludes:DestinationIp` `field:"DestinationIp" value:"20.0.0.0/11"`
`DestinationIp`	cidr_match	`::1/128`	`excludes:DestinationIp` `field:"DestinationIp" value:"::1/128"`
`DestinationIp`	cidr_match	`fc00::/7`	`excludes:DestinationIp` `field:"DestinationIp" value:"fc00::/7"`
`DestinationIp`	cidr_match	`fe80::/10`	`excludes:DestinationIp` `field:"DestinationIp" value:"fe80::/10"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\cscript.exe` corpus 72 (sigma 72) `\wscript.exe` corpus 74 (sigma 74)	`field:"Image" kind:ends_with`
`Initiated`	eq	`true` corpus 50 (sigma 50)	`field:"Initiated" kind:eq value:"true"`