Linux Base64 Encoded Pipe to Shell

Status: test
Severity: medium
Log source: category process_creation, product linux
Author: pH-T (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects suspicious process command line that uses base64 encoded input for execution with a shell

Known false positives

Legitimate administration activities

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1140` Deobfuscate/Decode Files or Information

Telemetry coverage

Platform	Record / event type
Linux	Event ID 1: Process Create

Rule body

title: Linux Base64 Encoded Pipe to Shell
id: ba592c6d-6888-43c3-b8c6-689b8fe47337
status: test
description: Detects suspicious process command line that uses base64 encoded input for execution with a shell
references:
    - https://github.com/arget13/DDexec
    - https://www.mandiant.com/resources/blog/barracuda-esg-exploited-globally
author: pH-T (Nextron Systems)
date: 2022-07-26
modified: 2023-06-16
tags:
    - attack.stealth
    - attack.t1140
logsource:
    product: linux
    category: process_creation
detection:
    selection_base64:
        CommandLine|contains: 'base64 '
    selection_exec:
        - CommandLine|contains:
              - '| bash '
              - '| sh '
              - '|bash '
              - '|sh '
        - CommandLine|endswith:
              - ' |sh'
              - '| bash'
              - '| sh'
              - '|bash'
    condition: all of selection_*
falsepositives:
    - Legitimate administration activities
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_base64`

selection_base64:
    CommandLine|contains: 'base64 '

Stage 2: `selection_exec`

selection_exec:
    - CommandLine|contains:
          - '| bash '
          - '| sh '
          - '|bash '
          - '|sh '
    - CommandLine|endswith:
          - ' |sh'
          - '| bash'
          - '| sh'
          - '|bash'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	ends_with	`\|sh` `\| bash` `\| sh` `\|bash`	`field:"CommandLine" kind:ends_with`
`CommandLine`	match	`base64` `\| bash` `\| sh` `\|bash` `\|sh`	`field:"CommandLine" kind:match`

Linux Base64 Encoded Pipe to Shell

Known false positives

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_base64

Stage 2: selection_exec

Indicators

Stage 0: `condition`

Stage 1: `selection_base64`

Stage 2: `selection_exec`