Suspicious Filename with Embedded Base64 Commands — Sigma Rule

Rule metadata and linked tags

Author: @kostastsale. Source status: experimental; severity: high. Source dates: 2025-11-22 / not supplied.

{
  "product": "linux",
  "category": "file_event"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: eb51bc041d739889ecbd52c5a3aa9e44e9d034fa123596cbb1c0b4b1d26edf28

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 Filename with Embedded Base64 Commands
id: 179b3686-6271-4d87-807d-17d843a8af73
status: experimental
description: |
    Detects files with specially crafted filenames that embed Base64-encoded bash payloads designed to execute when processed by shell scripts.
    These filenames exploit shell interpretation quirks to trigger hidden commands, a technique observed in VShell malware campaigns.
references:
    - https://www.trellix.com/blogs/research/the-silent-fileless-threat-of-vshell/
author: '@kostastsale'
date: 2025-11-22
tags:
    - attack.execution
    - attack.stealth
    - attack.t1059.004
    - attack.t1027
logsource:
    product: linux
    category: file_event
detection:
    selection:
        TargetFilename|contains:
            - '{echo'
            - '{base64,-d}'
    condition: selection
falsepositives:
    - Legitimate files with similar naming patterns (very unlikely).
level: high

Original YAML and metadata in JSON

False positives

• Legitimate files with similar naming patterns (very unlikely).

Source references

• https://www.trellix.com/blogs/research/the-silent-fileless-threat-of-vshell/