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Executable File with Unusual Extension
editExecutable File with Unusual Extension
editIdentifies 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.
Rule type: eql
Rule indices:
- logs-endpoint.events.file-*
Severity: low
Risk score: 21
Runs every: 60m
Searches indices from: now-119m (Date Math format, see also Additional look-back time)
Maximum alerts per execution: 100
References: None
Tags:
- Domain: Endpoint
- OS: Windows
- Use Case: Threat Detection
- Tactic: Defense Evasion
- Rule Type: BBR
- Data Source: Elastic Defend
Version: 2
Rule authors:
- Elastic
Rule license: Elastic License v2
Rule query
editfile 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"
Framework: MITRE ATT&CKTM
-
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/
-
Sub-technique:
- Name: Masquerade File Type
- ID: T1036.008
- Reference URL: https://attack.mitre.org/techniques/T1036/008/