IMPORTANT: No additional bug fixes or documentation updates
will be released for this version. For the latest information, see the
current release documentation.
Suspicious HTML File Creationedit
Identifies 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 guideedit
Rule queryedit
sequence 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 mappingedit
Framework: 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 historyedit
- Version 100 (8.5.0 release)
-
- Formatting only