SNAKE Malware WerFault Persistence File Creation

Status: test
Severity: high
Log source: category file_event, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the creation of a file named "WerFault.exe" in the WinSxS directory by a non-system process, which can be indicative of potential SNAKE malware activity

MITRE ATT&CK coverage

Tactic	Techniques
Execution	No specific technique

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 11: FileCreate

Rule body

title: SNAKE Malware WerFault Persistence File Creation
id: 64827580-e4c3-4c64-97eb-c72325d45399
status: test
description: Detects the creation of a file named "WerFault.exe" in the WinSxS directory by a non-system process, which can be indicative of potential SNAKE malware activity
references:
    - https://media.defense.gov/2023/May/09/2003218554/-1/-1/0/JOINT_CSA_HUNTING_RU_INTEL_SNAKE_MALWARE_20230509.PDF
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-05-10
modified: 2023-05-18
tags:
    - attack.execution
    - detection.emerging-threats
logsource:
    category: file_event
    product: windows
detection:
    selection:
        TargetFilename|startswith: 'C:\Windows\WinSxS\'
        TargetFilename|endswith: '\WerFault.exe'
    filter_main_system_location:
        Image|startswith:
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
            - 'C:\Windows\WinSxS\'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    TargetFilename|startswith: 'C:\Windows\WinSxS\'
    TargetFilename|endswith: '\WerFault.exe'

Stage 2: `not filter_main_system_location`

filter_main_system_location:
    Image|startswith:
        - 'C:\Windows\System32\'
        - 'C:\Windows\SysWOW64\'
        - 'C:\Windows\WinSxS\'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	starts_with	`C:\Windows\SysWOW64\`	`excludes:Image` `field:"Image" value:"C:\Windows\SysWOW64\"`
`Image`	starts_with	`C:\Windows\System32\`	`excludes:Image` `field:"Image" value:"C:\Windows\System32\"`
`Image`	starts_with	`C:\Windows\WinSxS\`	`excludes:Image` `field:"Image" value:"C:\Windows\WinSxS\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`TargetFilename`	ends_with	`\WerFault.exe` corpus 3 (sigma 3)	`field:"TargetFilename" kind:ends_with value:"\WerFault.exe"`
`TargetFilename`	starts_with	`C:\Windows\WinSxS\` corpus 2 (sigma 2)	`field:"TargetFilename" kind:starts_with value:"C:\Windows\WinSxS\"`