Suspicious Child Process of AspNetCompiler

calendar Oct 18, 2023 · attack.defense_evasion attack.t1127  ·
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Detects potentially suspicious child processes of "aspnet_compiler.exe".

Sigma rule (View on GitHub)

 1title: Suspicious Child Process of AspNetCompiler
 2id: 9ccba514-7cb6-4c5c-b377-700758f2f120 # SuspChild
 3related:
 4    - id: 4c7f49ee-2638-43bb-b85b-ce676c30b260 # TMP File
 5      type: similar
 6    - id: 9f50fe98-fe5c-4a2d-86c7-fad7f63ed622 # Susp Paths
 7      type: similar
 8    - id: a01b8329-5953-4f73-ae2d-aa01e1f35f00 # Exec
 9      type: similar
10status: experimental
11description: Detects potentially suspicious child processes of "aspnet_compiler.exe".
12references:
13    - https://lolbas-project.github.io/lolbas/Binaries/Aspnet_Compiler/
14    - https://ijustwannared.team/2020/08/01/the-curious-case-of-aspnet_compiler-exe/
15author: Nasreddine Bencherchali (Nextron Systems)
16date: 2023/08/14
17tags:
18    - attack.defense_evasion
19    - attack.t1127
20logsource:
21    category: process_creation
22    product: windows
23detection:
24    selection_parent:
25        ParentImage|endswith: '\aspnet_compiler.exe'
26    selection_child:
27        # Note: add other potential suspicious child processes and paths
28        - Image|endswith:
29              - '\calc.exe'
30              - '\notepad.exe'
31        - Image|contains:
32              - '\Users\Public\'
33              - '\AppData\Local\Temp\'
34              - '\AppData\Local\Roaming\'
35              - ':\Temp\'
36              - ':\Windows\Temp\'
37              - ':\Windows\System32\Tasks\'
38              - ':\Windows\Tasks\'
39    condition: all of selection_*
40falsepositives:
41    - Unknown
42level: high

References

  • Aspnet_compiler | LOLBAS

    Execute C# code with the Build Provider and proper folder structure in place. C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_compiler.exe -v none -p C:\users\cpl.internal\desktop\asptest\ -...


    Read More

  • The Curious Case of Aspnet_Compiler.exe

    Hey all, This post will explore code execution with aspnet_compiler.exe. I’m going to outline how to use the Microsoft signed executable to load & execute a local DLL builder and quickly …


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