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Suspicious HTML File Creation
editSuspicious HTML File Creation
editIdentifies the execution of a browser process to open an HTML file with high entropy and size. Adversaries may smuggle data and files past content filters by hiding malicious payloads inside of seemingly benign HTML files.
Rule type: eql
Rule indices:
- logs-endpoint.events.*
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
- Initial Access
Version: 100 (version history)
Added (Elastic Stack release): 8.4.0
Last modified (Elastic Stack release): 8.5.0
Rule authors: Elastic
Rule license: Elastic License v2
Investigation guide
editRule query
editsequence by user.id with maxspan=5m [file where event.action in ("creation", "rename") and file.extension : ("htm", "html") and file.path : ("?:\\Users\\*\\Downloads\\*", "?:\\Users\\*\\Content.Outlook\\*", "?:\\Users\\*\\AppData\\Local\\Temp\\Temp?_*", "?:\\Users\\*\\AppData\\Local\\Temp\\7z*", "?:\\Users\\*\\AppData\\Local\\Temp\\Rar$*") and ((file.Ext.entropy >= 5 and file.size >= 150000) or file.size >= 1000000)] [process where event.action == "start" and ( (process.name in ("chrome.exe", "msedge.exe", "brave.exe", "whale.exe", "browser.exe", "dragon.exe", "vivaldi.exe", "opera.exe") and process.args == "-- single-argument") or (process.name == "iexplore.exe" and process.args_count == 2) or (process.name in ("firefox.exe", "waterfox.exe") and process.args == "-url") ) and process.args : ("?:\\Users\\*\\Downloads\\*.htm*", "?:\\Users\\*\\Content.Outlook\\*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\Temp?_*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\7z*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\Rar$*.htm*")]
Threat mapping
editFramework: MITRE ATT&CKTM
-
Tactic:
- Name: Initial Access
- ID: TA0001
- Reference URL: https://attack.mitre.org/tactics/TA0001/
-
Technique:
- Name: Phishing
- ID: T1566
- Reference URL: https://attack.mitre.org/techniques/T1566/
-
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
edit- Version 100 (8.5.0 release)
-
- Formatting only