Executable File with Unusual Extension
ELASTIC detection rule by Elastic · Elastic License v2
Identifies the creation or modification of an executable file with an unexpected file extension. Attackers may attempt
to evade detection by masquerading files using the file extension values used by image, audio, or document file types.
[metadata]
creation_date = "2023/09/25"
integration = ["endpoint"]
maturity = "production"
updated_date = "2024/05/21"
[rule]
author = ["Elastic"]
building_block_type = "default"
description = """
Identifies the creation or modification of an executable file with an unexpected file extension. Attackers may attempt
to evade detection by masquerading files using the file extension values used by image, audio, or document file types.
"""
from = "now-119m"
index = ["logs-endpoint.events.file-*"]
interval = "60m"
language = "eql"
license = "Elastic License v2"
name = "Executable File with Unusual Extension"
risk_score = 21
rule_id = "ecd4857b-5bac-455e-a7c9-a88b66e56a9e"
severity = "low"
tags = [
"Domain: Endpoint",
"OS: Windows",
"Use Case: Threat Detection",
"Tactic: Defense Evasion",
"Rule Type: BBR",
"Data Source: Elastic Defend",
]
timestamp_override = "event.ingested"
type = "eql"
query = '''
file where host.os.type == "windows" and event.action != "deletion" and
/* MZ header or its common base64 equivalent TVqQ */
file.Ext.header_bytes : ("4d5a*", "54567151*") and
(
/* common image file extensions */
file.extension : ("jpg", "jpeg", "emf", "tiff", "gif", "png", "bmp", "fpx", "eps", "svg", "inf") or
/* common audio and video file extensions */
file.extension : ("mp3", "wav", "avi", "mpeg", "flv", "wma", "wmv", "mov", "mp4", "3gp") or
/* common document file extensions */
file.extension : ("txt", "pdf", "doc", "docx", "rtf", "ppt", "pptx", "xls", "xlsx", "hwp", "html")
) and
not process.pid == 4 and
not process.executable : "?:\\Program Files (x86)\\Trend Micro\\Client Server Security Agent\\Ntrtscan.exe"
'''
[[rule.threat]]
framework = "MITRE ATT&CK"
[[rule.threat.technique]]
id = "T1036"
name = "Masquerading"
reference = "https://attack.mitre.org/techniques/T1036/"
[[rule.threat.technique.subtechnique]]
id = "T1036.008"
name = "Masquerade File Type"
reference = "https://attack.mitre.org/techniques/T1036/008/"
[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"