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Detection rules › Sigma

Dynamic CSharp Compile Artefact

Status
test
Severity
low
Log source
product windows, category file_event
Author
frack113
Source
github.com/SigmaHQ/sigma

When C# is compiled dynamically, a .cmdline file will be created as a part of the process. Certain processes are not typically observed compiling C# code, but can do so without touching disk. This can be used to unpack a payload for execution

MITRE ATT&CK coverage

TacticTechniques
StealthT1027.004 Obfuscated Files or Information: Compile After Delivery

Event coverage

ProviderEventTitle
SysmonEvent ID 11FileCreate

Rule body yaml

title: Dynamic CSharp Compile Artefact
id: e4a74e34-ecde-4aab-b2fb-9112dd01aed0
status: test
description: |
    When C# is compiled dynamically, a .cmdline file will be created as a part of the process.
    Certain processes are not typically observed compiling C# code, but can do so without touching disk.
    This can be used to unpack a payload for execution
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1027.004/T1027.004.md#atomic-test-2---dynamic-c-compile
author: frack113
date: 2022-01-09
modified: 2023-02-17
tags:
    - attack.stealth
    - attack.t1027.004
logsource:
    product: windows
    category: file_event
detection:
    selection:
        TargetFilename|endswith: '.cmdline'
    condition: selection
falsepositives:
    - Unknown
level: low

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    TargetFilename|endswith: '.cmdline'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
TargetFilenameends_with
  • .cmdline