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: 5m
Searches indices from: now-9m (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: Initial Access
- Data Source: Elastic Defend
Version: 106
Rule authors:
- Elastic
Rule license: Elastic License v2
Setup
editSetup
If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2,
events will not define event.ingested
and default fallback for EQL rules was not added until version 8.2.
Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate
event.ingested
to @timestamp.
For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html
Rule query
editsequence by user.id with maxspan=5m [file where host.os.type == "windows" and 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$*") and ((file.Ext.entropy >= 5 and file.size >= 150000) or file.size >= 1000000)] [process where host.os.type == "windows" and event.action == "start" and ( (process.name in ("chrome.exe", "msedge.exe", "brave.exe", "whale.exe", "browser.exe", "dragon.exe", "vivaldi.exe", "opera.exe") and process.args == "--single-argument") or (process.name == "iexplore.exe" and process.args_count == 2) or (process.name in ("firefox.exe", "waterfox.exe") and process.args == "-url") ) and process.args : ("?:\\Users\\*\\Downloads\\*.htm*", "?:\\Users\\*\\Content.Outlook\\*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\Temp?_*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\7z*.htm*", "?:\\Users\\*\\AppData\\Local\\Temp\\Rar$*.htm*")]
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/
-
Sub-technique:
- Name: Spearphishing Attachment
- ID: T1566.001
- Reference URL: https://attack.mitre.org/techniques/T1566/001/
-
Sub-technique:
- Name: Spearphishing Link
- ID: T1566.002
- Reference URL: https://attack.mitre.org/techniques/T1566/002/
-
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/
-
Sub-technique:
- Name: HTML Smuggling
- ID: T1027.006
- Reference URL: https://attack.mitre.org/techniques/T1027/006/