Suspicious Csi.exe Usage

calendar Aug 12, 2024 · attack.execution attack.t1072 attack.defense-evasion attack.t1218  ·
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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'

Sigma rule (View on GitHub)

 1title: Suspicious Csi.exe Usage
 2id: 40b95d31-1afc-469e-8d34-9a3a667d058e
 3status: test
 4description: 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'
 5references:
 6    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Csi/
 7    - https://lolbas-project.github.io/lolbas/OtherMSBinaries/Rcsi/
 8    - https://enigma0x3.net/2016/11/21/bypassing-application-whitelisting-by-using-rcsi-exe/
 9    - https://twitter.com/Z3Jpa29z/status/1317545798981324801
10author: Konstantin Grishchenko, oscd.community
11date: 2020-10-17
12modified: 2022-07-11
13tags:
14    - attack.execution
15    - attack.t1072
16    - attack.defense-evasion
17    - attack.t1218
18logsource:
19    category: process_creation
20    product: windows
21detection:
22    selection_img:
23        - Image|endswith:
24              - '\csi.exe'
25              - '\rcsi.exe'
26        - OriginalFileName:
27              - 'csi.exe'
28              - 'rcsi.exe'
29    selection_cli:
30        Company: 'Microsoft Corporation'
31    condition: all of selection*
32fields:
33    - ComputerName
34    - User
35    - CommandLine
36    - ParentCommandLine
37falsepositives:
38    - Legitimate usage by software developers
39level: medium

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