Windows Rundll32 WebDAV Request

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Description

The following analytic identifies rundll32.exe with the commandline arguments loading davclnt.dll function - davsetcookie - to be used to access a remote WebDav instance. This particular behavior was recently showcased in CVE-2023-23397.

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint
• Last Updated: 2023-03-15
• Author: Michael Haag, Splunk
• ID: 320099b7-7eb1-4153-a2b4-decb53267de2

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1048.003	Exfiltration Over Unencrypted Non-C2 Protocol	Exfiltration

Kill Chain Phase

• Actions On Objectives

NIST

• DE.CM

CIS20

• CIS 10

CVE

ID	Summary	CVSS
CVE-2023-23397	Microsoft Outlook Elevation of Privilege Vulnerability	None

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name=rundll32.exe Processes.process IN ("*\\windows\\system32\\davclnt.dll,*davsetcookie*","*\\windows\\syswow64\\davclnt.dll,*davsetcookie*") by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_rundll32_webdav_request_filter`

Macros

The SPL above uses the following Macros:

• security_content_summariesonly
• security_content_ctime

windows_rundll32_webdav_request_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
• Processes.dest
• Processes.user
• Processes.parent_process_name
• Processes.parent_process
• Processes.original_file_name
• Processes.process_name
• Processes.process
• Processes.process_id
• Processes.parent_process_path
• Processes.process_path
• Processes.parent_process_id

How To Implement

In addition to getting the correct data, adding a join with network connection will assist with making this higher fidelity. We removed the parent_process_name=svchost.exe to look more broad, this will need to be tuned. 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. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

False positives will be present based on legitimate software, filtering may need to occur.

Associated Analytic Story

• CVE-2023-23397 Outlook Elevation of Privilege

RBA

Risk Score	Impact	Confidence	Message
48.0	80	60	An instance of $parent_process_name$ spawning $process_name$ was identified on endpoint $dest$ by user $user$ attempting to contact a remote WebDav server.

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://strontic.github.io/xcyclopedia/library/davclnt.dll-0EA3050E7CC710526E330C413C165DA0.html
• https://twitter.com/ACEResponder/status/1636116096506818562?s=20
• https://twitter.com/domchell/status/1635999068282408962?s=20
• https://msrc.microsoft.com/blog/2023/03/microsoft-mitigates-outlook-elevation-of-privilege-vulnerability/
• https://www.pwndefend.com/2023/03/15/the-long-game-persistent-hash-theft/

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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