Windows: Alert on csc.exe Executing from User-Writable or Suspicious Paths
Alerts when csc.exe is launched from user/temp-like paths, indicating potential on-the-fly .NET compilation.
FreeReviewedSigma · Medium · v2
- Product
- windows
- Category
- process_creation
- Author
- Florian Roth (Nextron Systems), X__Junior (Nextron Systems) (SigmaHQ), DRL 1.1
- Published
- 2019-08-24
- Updated
- 2026-07-31
ATT&CK techniques
Defense EvasionRecon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact
What it detects
This rule flags process executions of csc.exe when command-line arguments indicate the compiler is being run from or interacting with user-writable and commonly abused locations (for example, Temp, Perflogs, or Temporary Internet) or specific user directory targets. Compiling .NET code on the fly can enable stealthy staging and follow-on payload execution, so identifying csc.exe launched with suspicious path context is important. It relies on process creation telemetry including Image ending with csc.exe, command-line contents, and parent process context for multiple exclusions.
Reporting behind it
- securityboulevard.comhttps://securityboulevard.com/2019/08/agent-tesla-evading-edr-by-removing-api-hooks/
- clearskysec.comhttps://www.clearskysec.com/wp-content/uploads/2018/11/MuddyWater-Operations-in-Lebanon-and-Oman.pdf
- app.any.runhttps://app.any.run/tasks/c6993447-d1d8-414e-b856-675325e5aa09/
- twitter.comhttps://twitter.com/gN3mes1s/status/1206874118282448897
- github.comhttps://github.com/redcanaryco/atomic-red-team/blob/b27a3cb25025161d49ac861cb216db68c46a3537/atomics/T1027.004/T1027.004.md#atomic-test-1---compile-after-delivery-using-cscexe
- github.comhttps://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_csc_susp_dynamic_compilation.yml
Changelog
v2- v2Candidate ingested via manual entry.2026-07-31
- v1No changelog recorded for this version.2026-07-30
Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.
windows-process-creation-detecting-csc-exe-used-to-compile-net-code-dcaa3f04
title: "Windows: Alert on csc.exe Executing from User-Writable or Suspicious Paths"
id: 69ff7134-baf0-4d40-b387-00a55f329b85
status: test
description: This rule flags process executions of csc.exe when command-line arguments indicate the compiler is being run from or interacting with user-writable and commonly abused locations (for example, Temp, Perflogs, or Temporary Internet) or specific user directory targets. Compiling .NET code on the fly can enable stealthy staging and follow-on payload execution, so identifying csc.exe launched with suspicious path context is important. It relies on process creation telemetry including Image ending with csc.exe, command-line contents, and parent process context for multiple exclusions.
references:
- https://securityboulevard.com/2019/08/agent-tesla-evading-edr-by-removing-api-hooks/
- https://www.clearskysec.com/wp-content/uploads/2018/11/MuddyWater-Operations-in-Lebanon-and-Oman.pdf
- https://app.any.run/tasks/c6993447-d1d8-414e-b856-675325e5aa09/
- https://twitter.com/gN3mes1s/status/1206874118282448897
- https://github.com/redcanaryco/atomic-red-team/blob/b27a3cb25025161d49ac861cb216db68c46a3537/atomics/T1027.004/T1027.004.md#atomic-test-1---compile-after-delivery-using-cscexe
- https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_csc_susp_dynamic_compilation.yml
author: Florian Roth (Nextron Systems), X__Junior (Nextron Systems), Huntrule Team
date: 2019-08-24
modified: 2026-03-23
tags:
- attack.stealth
- attack.t1027.004
logsource:
category: process_creation
product: windows
detection:
selection_img:
Image|endswith: \csc.exe
selection_susp_location_1:
CommandLine|contains:
- :\Perflogs\
- :\Users\Public\
- \AppData\Local\Temp\
- \Temporary Internet
- \Windows\Temp\
selection_susp_location_2:
- CommandLine|contains|all:
- :\Users\
- \Favorites\
- CommandLine|contains|all:
- :\Users\
- \Favourites\
- CommandLine|contains|all:
- :\Users\
- \Contacts\
- CommandLine|contains|all:
- :\Users\
- \Pictures\
selection_susp_location_3:
CommandLine|re: (?:[Pp]rogram[Dd]ata|%(?:[Ll]ocal)?[Aa]pp[Dd]ata%|\\[Aa]pp[Dd]ata\\(?:[Ll]ocal(?:[Ll]ow)?|[Rr]oaming))\\[^\\]{1,256}$
filter_main_programfiles:
ParentImage|startswith:
- C:\Program Files (x86)\
- C:\Program Files\
filter_main_sdiagnhost:
ParentImage: C:\Windows\System32\sdiagnhost.exe
filter_main_w3p:
ParentImage: C:\Windows\System32\inetsrv\w3wp.exe
filter_optional_chocolatey:
ParentImage:
- C:\ProgramData\chocolatey\choco.exe
- C:\ProgramData\chocolatey\tools\shimgen.exe
filter_optional_defender:
ParentCommandLine|contains: \ProgramData\Microsoft\Windows Defender Advanced Threat Protection
filter_optional_ansible:
ParentCommandLine|contains:
- JwB7ACIAZgBhAGkAbABlAGQAIgA6AHQAcgB1AGUALAAiAG0AcwBnACIAOgAiAEEAbgBzAGkAYgBsAGUAIAByAGUAcQB1AGkAcgBlAHMAIABQAG8AdwBlAHIAUwBoAGUAbABsACAAdgAzAC4AMAAgAG8AcgAgAG4AZQB3AGUAcgAiAH0AJw
- cAewAiAGYAYQBpAGwAZQBkACIAOgB0AHIAdQBlACwAIgBtAHMAZwAiADoAIgBBAG4AcwBpAGIAbABlACAAcgBlAHEAdQBpAHIAZQBzACAAUABvAHcAZQByAFMAaABlAGwAbAAgAHYAMwAuADAAIABvAHIAIABuAGUAdwBlAHIAIgB9ACcA
- nAHsAIgBmAGEAaQBsAGUAZAAiADoAdAByAHUAZQAsACIAbQBzAGcAIgA6ACIAQQBuAHMAaQBiAGwAZQAgAHIAZQBxAHUAaQByAGUAcwAgAFAAbwB3AGUAcgBTAGgAZQBsAGwAIAB2ADMALgAwACAAbwByACAAbgBlAHcAZQByACIAfQAnA
condition: selection_img and 1 of selection_susp_location_* and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
- Legitimate software from program files - https://twitter.com/gN3mes1s/status/1206874118282448897
- Legitimate Microsoft software - https://twitter.com/gabriele_pippi/status/1206907900268072962
- Ansible
level: medium
license: DRL-1.1
related:
- id: dcaa3f04-70c3-427a-80b4-b870d73c94c4
type: derived