IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

« Privilege Escalation via Windir Environment Variable Process Execution from an Unusual Directory »

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Process Activity via Compiled HTML File

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Process Activity via Compiled HTML File

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Compiled HTML files (.chm) are commonly distributed as part of the Microsoft HTML Help system. Adversaries may conceal malicious code in a CHM file and deliver it to a victim for execution. CHM content is loaded by the HTML Help executable program (hh.exe).

Rule type: eql

Rule indices:

winlogbeat-*
logs-endpoint.events.*
logs-windows.*

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
Execution

Version: 13 (version history)

Added (Elastic Stack release): 7.6.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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The HTML Help executable program (hh.exe) runs whenever a user clicks a compiled help (.chm) file or menu item that opens the help file inside the Help Viewer. This is not always malicious, but adversaries may abuse this technology to conceal malicious code.

Investigation guide

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Rule query

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process where event.type in ("start", "process_started") and
process.parent.name : "hh.exe" and process.name : ("mshta.exe",
"cmd.exe", "powershell.exe", "pwsh.exe", "powershell_ise.exe",
"cscript.exe", "wscript.exe")

Threat mapping

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Framework: MITRE ATT&CK^TM

Tactic:
- Name: Execution
- ID: TA0002
- Reference URL: https://attack.mitre.org/tactics/TA0002/
Technique:
- Name: User Execution
- ID: T1204
- Reference URL: https://attack.mitre.org/techniques/T1204/
Tactic:
- Name: Defense Evasion
- ID: TA0005
- Reference URL: https://attack.mitre.org/tactics/TA0005/
Technique:
- Name: System Binary Proxy Execution
- ID: T1218
- Reference URL: https://attack.mitre.org/techniques/T1218/

Rule version history

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Version 13 (8.4.0 release)

Updated query, changed from:

process where event.type in ("start", "process_started") and
process.parent.name : "hh.exe" and process.name : ("mshta.exe",
"cmd.exe", "powershell.exe", "pwsh.exe", "powershell_ise.exe",
"cscript.exe", "wscript.exe")

Version 11 (8.2.0 release)

Formatting only

Version 10 (7.16.0 release)

Updated query, changed from:

process where event.type in ("start", "process_started") and
process.parent.name : "hh.exe" and process.name : ("mshta.exe",
"cmd.exe", "powershell.exe", "pwsh.exe", "cscript.exe", "wscript.exe")

Version 8 (7.13.0 release)

Updated query, changed from:

event.category:process and event.type:(start or process_started) and
process.name:hh.exe

Version 7 (7.12.0 release)

Formatting only

Version 6 (7.11.2 release)

Formatting only

Version 5 (7.11.0 release)

Formatting only

Version 4 (7.10.0 release)

Updated query, changed from:
```
event.code:1 and process.name:hh.exe
```

Version 3 (7.9.0 release)

Formatting only

Version 2 (7.7.0 release)

Formatting only

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