MSHTML Module Load in Office Product

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Description

The following analytic detects the loading of the mshtml.dll module into an Office product, which is indicative of CVE-2021-40444 exploitation. It leverages Sysmon EventID 7 to monitor image loads by specific Office processes. This activity is significant because it can indicate an attempt to exploit a vulnerability in the MSHTML component via a malicious document. If confirmed malicious, this could allow an attacker to execute arbitrary code, potentially leading to system compromise, data exfiltration, or further network penetration.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2024-05-14
• Author: Michael Haag, Mauricio Velazco, Splunk
• ID: 5f1c168e-118b-11ec-84ff-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1566	Phishing	Initial Access

T1566.001

Spearphishing Attachment

Initial Access

Kill Chain Phase

• Delivery

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`sysmon` EventID=7 process_name IN ("winword.exe","excel.exe","powerpnt.exe","mspub.exe","visio.exe","wordpad.exe","wordview.exe","onenote.exe","onenotem.exe","onenoteviewer.exe","onenoteim.exe", "msaccess.exe","Graph.exe","winproj.exe") loaded_file_path IN ("*\\mshtml.dll", "*\\Microsoft.mshtml.dll","*\\IE.Interop.MSHTML.dll","*\\MshtmlDac.dll","*\\MshtmlDed.dll","*\\MshtmlDer.dll") 
| stats count min(_time) as firstTime max(_time) as lastTime by user_id, dest, process_name, loaded_file, loaded_file_path, original_file_name, process_guid 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `mshtml_module_load_in_office_product_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• sysmon

mshtml_module_load_in_office_product_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• _time
• ImageLoaded
• process_name
• OriginalFileName
• process_id
• dest

How To Implement

To successfully implement this search, you need to be ingesting logs with the process names and image loads from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

Limited false positives will be present, however, tune as necessary. Some applications may legitimately load mshtml.dll.

Associated Analytic Story

• Spearphishing Attachments
• Microsoft MSHTML Remote Code Execution CVE-2021-40444
• CVE-2023-36884 Office and Windows HTML RCE Vulnerability

RBA

Risk Score	Impact	Confidence	Message
80.0	80	100	An instance of $process_name$ was identified on endpoint $dest$ loading mshtml.dll.

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• https://app.any.run/tasks/36c14029-9df8-439c-bba0-45f2643b0c70/
• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
• https://strontic.github.io/xcyclopedia/index-dll
• https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/trojanized-onenote-document-leads-to-formbook-malware/

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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