sigmamediumHunting

Suspicious Csi.exe Usage

Csi.exe is a signed binary from Microsoft that comes with Visual Studio and provides C# interactive capabilities. It can be used to run C# code from a file passed as a parameter in command line. Early version of this utility provided with Microsoft “Roslyn” Community Technology Preview was named 'rcsi.exe'

MITRE ATT&CK

T1072 T1218

lateral-movementexecutiondefense-evasion

Detection Query

selection_img:
  - Image|endswith:
      - \csi.exe
      - \rcsi.exe
  - OriginalFileName:
      - csi.exe
      - rcsi.exe
selection_cli:
  Company: Microsoft Corporation
condition: all of selection*

Author

Konstantin Grishchenko, oscd.community

Created

2020-10-17

Data Sources

windowsProcess Creation Events

Platforms

windows

References

Tags

attack.lateral-movementattack.executionattack.t1072attack.defense-evasionattack.t1218

Raw Content

title: Suspicious Csi.exe Usage
id: 40b95d31-1afc-469e-8d34-9a3a667d058e
status: test
description: Csi.exe is a signed binary from Microsoft that comes with Visual Studio and provides C# interactive capabilities. It can be used to run C# code from a file passed as a parameter in command line. Early version of this utility provided with Microsoft “Roslyn” Community Technology Preview was named 'rcsi.exe'
references:
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Csi/
    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Rcsi/
    - https://enigma0x3.net/2016/11/21/bypassing-application-whitelisting-by-using-rcsi-exe/
    - https://twitter.com/Z3Jpa29z/status/1317545798981324801
author: Konstantin Grishchenko, oscd.community
date: 2020-10-17
modified: 2022-07-11
tags:
    - attack.lateral-movement
    - attack.execution
    - attack.t1072
    - attack.defense-evasion
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\csi.exe'
              - '\rcsi.exe'
        - OriginalFileName:
              - 'csi.exe'
              - 'rcsi.exe'
    selection_cli:
        Company: 'Microsoft Corporation'
    condition: all of selection*
falsepositives:
    - Legitimate usage by software developers
level: medium