sigma-rules/rules/windows/defense_evasion_execution_msbuild_started_unusal_process.toml

[metadata]
creation_date = "2020/03/25"
integration = ["endpoint", "windows", "system"]
maturity = "production"
min_stack_comments = "Multiple field support in the New Terms rule type was added in Elastic 8.6"
min_stack_version = "8.6.0"
updated_date = "2024/01/16"

[rule]
author = ["Elastic"]
description = """
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.
"""
false_positives = [
    """
    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.
    """,
]
from = "now-9m"
index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*", "logs-system.security*"]
language = "kuery"
license = "Elastic License v2"
name = "Microsoft Build Engine Started an Unusual Process"
references = ["https://blog.talosintelligence.com/2020/02/building-bypass-with-msbuild.html"]
risk_score = 21
rule_id = "9d110cb3-5f4b-4c9a-b9f5-53f0a1707ae6"
setup = """

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
events will not define `event.ingested` and default fallback for EQL rules was not added until version 8.2.
Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
`event.ingested` to @timestamp.
For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
"""
severity = "low"
tags = ["Domain: Endpoint",
        "OS: Windows",
        "Use Case: Threat Detection",
        "Tactic: Defense Evasion",
        "Tactic: Execution",
        "Data Source: Elastic Defend"
        ]

timestamp_override = "event.ingested"
type = "new_terms"

query = '''
host.os.type:windows and event.category:process and event.type:start and process.parent.name:("MSBuild.exe" or "msbuild.exe") and
process.name:("csc.exe" or "iexplore.exe" or "powershell.exe")
'''

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1027"
name = "Obfuscated Files or Information"
reference = "https://attack.mitre.org/techniques/T1027/"

[[rule.threat.technique.subtechnique]]
id = "T1027.004"
name = "Compile After Delivery"
reference = "https://attack.mitre.org/techniques/T1027/004/"

[[rule.threat.technique]]
id = "T1127"
name = "Trusted Developer Utilities Proxy Execution"
reference = "https://attack.mitre.org/techniques/T1127/"
[[rule.threat.technique.subtechnique]]
id = "T1127.001"
name = "MSBuild"
reference = "https://attack.mitre.org/techniques/T1127/001/"



[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"

[rule.new_terms]
field = "new_terms_fields"
value = ["host.id", "user.name"]

[[rule.new_terms.history_window_start]]
field = "history_window_start"
value = "now-14d"