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Description

The following analytic identifies behavior related to CVE-2021-40444. Whereas the malicious document will load ActiveX and download the remote payload (.inf, .cab). During triage, review parallel processes and further activity on endpoint to identify additional patterns. Retrieve the file modifications and analyze further.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint
  • Last Updated: 2023-02-15
  • Author: Michael Haag, Splunk
  • ID: f48cd1d4-125a-11ec-a447-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

| ID | Summary | CVSS | | ———– | ———– | ————– | | CVE-2021-40444 | <p>Microsoft is investigating reports of a remote code execution vulnerability in MSHTML that affects Microsoft Windows. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability by using specially-crafted Microsoft Office documents.</p> <p>An attacker could craft a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights.</p> <p>Microsoft Defender Antivirus and Microsoft Defender for Endpoint both provide detection and protections for the known vulnerability. Customers should keep antimalware products up to date. Customers who utilize automatic updates do not need to take additional action. Enterprise customers who manage updates should select the detection build 1.349.22.0 or newer and deploy it across their environments. Microsoft Defender for Endpoint alerts will be displayed as: “Suspicious Cpl File Execution”.</p> <p>Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update through our monthly release process or providing an out-of-cycle security update, depending on customer needs.</p> <p>Please see the <strong>Mitigations</strong> and <strong>Workaround</strong> sections for important information about steps you can take to protect your system from this vulnerability.</p> <p><strong>UPDATE</strong> September 14, 2021: Microsoft has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. Please see the FAQ for important information about which updates are applicable to your system.</p> | 6.8 |



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| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.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") by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.process_guid 
| `drop_dm_object_name(Processes)` 
|rename process_guid as proc_guid 
| join proc_guid, _time [ 
| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_name IN ("*.inf","*.cab") by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.file_path Filesystem.process_guid 
| `drop_dm_object_name(Filesystem)` 
|rename process_guid as proc_guid 
| fields _time dest file_create_time file_name file_path process_name process_path process proc_guid] 
| dedup file_create_time 
| table dest, process_name, process, file_create_time, file_name, file_path, proc_guid 
| `office_product_writing_cab_or_inf_filter`

Macros

The SPL above uses the following Macros:

:information_source: office_product_writing_cab_or_inf_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
  • dest
  • process_name
  • process
  • file_create_time
  • file_name
  • file_path

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node and Filesystem node.

Known False Positives

The query is structured in a way that action (read, create) is not defined. Review the results of this query, filter, and tune as necessary. It may be necessary to generate this query specific to your endpoint product.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
80.0 80 100 An instance of $process_name$ was identified on $dest$ writing an inf or cab file to this. This is not typical of $process_name$.

:information_source: 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

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

source | version: 4