Detection: Windows Rundll32 Execution With Log.DLL

Description

Identifies the execution of rundll32 with a command line argument of "log.dll", as used in the Lotus Blossom Chrysalis backdoor campaign. Attackers placed a malicious "log.dll" in "%AppData%\Bluetooth" and invoked it via rundll32.exe "log.dll,LogInit" to decrypt and execute ShellCode. The legitimate Bitdefender Submission Wizard (BDSubmit.exe, bdsw.exe) also uses log.dll and is vulnerable to DLL sideloading.

Search

 1
 2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime
 3  from datamodel=Endpoint.Processes where
 4  `process_rundll32`
 5  Processes.process="* log.dll*"
 6  by Processes.action Processes.dest Processes.original_file_name Processes.parent_process Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id Processes.parent_process_name Processes.parent_process_path Processes.process Processes.process_exec Processes.process_guid Processes.process_hash Processes.process_id Processes.process_integrity_level Processes.process_name Processes.process_path Processes.user Processes.user_id Processes.vendor_product
 7
 8| `drop_dm_object_name(Processes)`
 9
10| `security_content_ctime(firstTime)`
11
12| `security_content_ctime(lastTime)`
13
14| `windows_rundll32_execution_with_log_dll_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4688	Windows	'XmlWinEventLog'	'XmlWinEventLog:Security'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

Ingest process creation logs (Sysmon EventID 1 or equivalent) and map them to the Endpoint.Processes data model. Ensure command-line arguments are captured so that "log.dll" appears in the process field. The Splunk Add-on for Microsoft Sysmon and CIM are required.

Known False Positives

Legitimate use of rundll32 to load log.dll from trusted locations may trigger this. Allowlist known paths or parent processes as needed.

Associated Analytic Story

• Lotus Blossom Chrysalis Backdoor

Intermediate Findings

Threat Objects

References

• https://www.rapid7.com/blog/post/tr-chrysalis-backdoor-dive-into-lotus-blossoms-toolkit/

• https://attack.mitre.org/techniques/T1574/002/

• https://attack.mitre.org/groups/G0065/

Detection Testing

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: GitHub | Version: 3