Suspicious Greedy Compression Using Rar.EXE — Sigma Rule

Rule metadata and linked tags

Author: X__Junior (Nextron Systems), Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2022-12-15 / 2024-01-02.

{
  "product": "windows",
  "category": "process_creation"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 6cb00a089f525cbbc99fbbfcef572838536e2a97e0d62ede0d08a9f25a0f3e7f

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Suspicious Greedy Compression Using Rar.EXE
id: afe52666-401e-4a02-b4ff-5d128990b8cb
status: test
description: Detects RAR usage that creates an archive from a suspicious folder, either a system folder or one of the folders often used by attackers for staging purposes
references:
    - https://decoded.avast.io/martinchlumecky/png-steganography
author: X__Junior (Nextron Systems), Florian Roth (Nextron Systems)
date: 2022-12-15
modified: 2024-01-02
tags:
    - attack.execution
    - attack.t1059
logsource:
    product: windows
    category: process_creation
detection:
    # Example : rar.exe a -m5 -r -y -ta20210204000000 -hp1qazxcde32ws -v2560k Asia1Dpt-PC-c.rar c:\\*.doc c:\\*.docx c:\\*.xls c:\\*.xlsx c:\\*.pdf c:\\*.ppt c:\\*.pptx c:\\*.jpg c:\\*.txt >nul
    selection_opt_1:
        - Image|endswith: '\rar.exe'
        - Description: 'Command line RAR'
    selection_opt_2:
        CommandLine|contains:
            - '.exe a '
            - ' a -m'
    selection_cli_flags:
        CommandLine|contains|all:
            - ' -hp' # password
            - ' -r ' # recursive
    selection_cli_folders:
        CommandLine|contains:
            - ' ?:\\\*.'
            - ' ?:\\\\\*.'
            - ' ?:\$Recycle.bin\'
            - ' ?:\PerfLogs\'
            - ' ?:\Temp'
            - ' ?:\Users\Public\'
            - ' ?:\Windows\'
            - ' %public%'
    condition: 1 of selection_opt_* and all of selection_cli_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://decoded.avast.io/martinchlumecky/png-steganography