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Executable File Creation with Multiple Extensions

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Executable File Creation with Multiple Extensions

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Masquerading can allow an adversary to evade defenses and better blend in with the environment. One way it occurs is when the name or location of a file is manipulated as a means of tricking a user into executing what they think is a benign file type but is actually executable code.

Rule type: eql

Rule indices:

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

Severity: medium

Risk score: 47

Runs every: 5 minutes

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

Maximum alerts per execution: 100

Tags:

Elastic
Host
Windows
Threat Detection
Defense Evasion

Version: 6 (version history)

Added (Elastic Stack release): 7.12.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic

Rule license: Elastic License v2

Investigation guide

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Rule query

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file where event.type == "creation" and file.extension : "exe" and
file.name regex~ """.*\.(vbs|vbe|bat|js|cmd|wsh|ps1|pdf|docx?|xlsx?|pp
tx?|txt|rtf|gif|jpg|png|bmp|hta|txt|img|iso)\.exe""" and not
(process.executable : ("?:\\Windows\\System32\\msiexec.exe",
"C:\\Users\\*\\QGIS_SCCM\\Files\\QGIS-OSGeo4W-*-Setup-x86_64.exe") and
file.path : "?:\\Program Files\\QGIS *\\apps\\grass\\*.exe") and not
process.executable : ("/bin/sh", "/usr/sbin/MailScanner",
"/usr/bin/perl")

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: Masquerading
- ID: T1036
- Reference URL: https://attack.mitre.org/techniques/T1036/
Tactic:
- Name: Execution
- ID: TA0002
- Reference URL: https://attack.mitre.org/tactics/TA0002/
Technique:
- Name: User Execution
- ID: T1204
- Reference URL: https://attack.mitre.org/techniques/T1204/

Rule version history

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Version 6 (8.4.0 release)

Updated query, changed from:

file where event.type == "creation" and file.extension : "exe" and
file.name regex~ """.*\.(vbs|vbe|bat|js|cmd|wsh|ps1|pdf|docx?|xlsx?|pp
tx?|txt|rtf|gif|jpg|png|bmp|hta|txt|img|iso)\.exe"""

Version 4 (8.2.0 release)

Formatting only

Version 3 (7.16.0 release)

Formatting only

Version 2 (7.14.0 release)

Updated query, changed from:

file where event.type == "creation" and file.extension:"exe" and
file.name: ( "*.vbs.exe", "*.vbe.exe", "*.bat.exe",
"*.js.exe", "*.cmd.exe", "*.wsh.exe", "*.ps1.exe",
"*.pdf.exe", "*.docx.exe", "*.doc.exe", "*.xlsx.exe",
"*.xls.exe", "*.pptx.exe", "*.ppt.exe", "*.txt.exe",
"*.rtf.exe", "*.gif.exe", "*.jpg.exe", "*.png.exe",
"*.bmp.exe", "*.hta.exe", "*.txt.exe", "*.img.exe",
"*.iso.exe" )

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