IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Microsoft Build Engine Started an Unusual Process

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Microsoft Build Engine Started an Unusual Process

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An instance of MSBuild, the Microsoft Build Engine, started a PowerShell script or the Visual C# Command Line Compiler. This technique is sometimes used to deploy a malicious payload using the Build Engine.

Rule type: eql

Rule indices:

winlogbeat-*
logs-endpoint.events.*
logs-windows.*

Severity: low

Risk score: 21

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

https://blog.talosintelligence.com/2020/02/building-bypass-with-msbuild.html

Tags:

Elastic
Host
Windows
Threat Detection
Defense Evasion

Version: 11 (version history)

Added (Elastic Stack release): 7.7.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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The Build Engine is commonly used by Windows developers but use by non-engineers is unusual. If a build system triggers this rule it can be exempted by process, user or host name.

Investigation guide

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Rule query

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process where event.type in ("start", "process_started") and
process.parent.name : "MSBuild.exe" and process.name : ("csc.exe",
"iexplore.exe", "powershell.exe")

Threat mapping

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Framework: MITRE ATT&CK^TM

Tactic:
- Name: Defense Evasion
- ID: TA0005
- Reference URL: https://attack.mitre.org/tactics/TA0005/
Technique:
- Name: Obfuscated Files or Information
- ID: T1027
- Reference URL: https://attack.mitre.org/techniques/T1027/

Rule version history

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Version 11 (8.4.0 release)

Formatting only

Version 9 (8.2.0 release)

Formatting only

Version 8 (7.13.0 release)

Updated query, changed from:

event.category:process and event.type:(start or process_started) and
process.parent.name:MSBuild.exe and process.name:(csc.exe or
iexplore.exe or powershell.exe)

Version 7 (7.12.0 release)

Formatting only

Version 6 (7.11.2 release)

Formatting only

Version 5 (7.11.0 release)

Formatting only

Version 4 (7.10.0 release)

Formatting only

Version 3 (7.9.1 release)

Formatting only

Version 2 (7.9.0 release)

Updated query, changed from:

process.parent.name:MSBuild.exe and process.name:(csc.exe or
iexplore.exe or powershell.exe)

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