Detection: Windows Unsigned MS DLL Side-Loading

Description

The following analytic identifies potential DLL side-loading instances involving unsigned DLLs mimicking Microsoft signatures. It detects this activity by analyzing Sysmon logs for Event Code 7, where both the Image and ImageLoaded paths do not match system directories like system32, syswow64, and programfiles. This behavior is significant as adversaries often exploit DLL side-loading to execute malicious code via legitimate processes. If confirmed malicious, this activity could allow attackers to execute arbitrary code, potentially leading to privilege escalation, persistence, and unauthorized access to sensitive information.

Search

1`sysmon` EventCode=7 Company="Microsoft Corporation" Signed=false SignatureStatus != Valid NOT (Image IN("C:\\Windows\\System32\\*", "C:\\Windows\\SysWow64\\*", "C:\\Program Files*")) NOT (ImageLoaded IN("C:\\Windows\\System32\\*", "C:\\Windows\\SysWow64\\*", "C:\\Program Files*")) 
2| rex field=Image "(?<ImageFolderPath>.+\\\)" 
3| rex field=ImageLoaded "(?<ImageLoadedFolderPath>.+\\\)" 
4| where ImageFolderPath = ImageLoadedFolderPath 
5| stats count min(_time) as firstTime max(_time) as lastTime by Image ProcessGuid ImageLoaded user Computer EventCode ImageFolderPath ImageLoadedFolderPath Company Description Product Signed SignatureStatus 
6| rename Computer as dest 
7| `security_content_ctime(firstTime)` 
8| `security_content_ctime(lastTime)` 
9| `windows_unsigned_ms_dll_side_loading_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 7	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

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

Implementation

The analytic is designed to be run against Sysmon event logs collected from endpoints. The analytic requires the Sysmon event logs to be ingested into Splunk. The analytic searches for EventCode 7 where the Image is either SQLDumper.exe or SQLWriter.exe and the ImageLoaded is vcruntime140.dll. The search also filters out the legitimate loading of vcruntime140.dll from the System32 directory to reduce false positives. The analytic can be modified to include additional known good paths for vcruntime140.dll to further reduce false positives.

Known False Positives

False positives are possible if legitimate processes are loading vcruntime140.dll from non-standard directories. It is recommended to investigate the context of the process loading vcruntime140.dll to determine if it is malicious or not. Modify the search to include additional known good paths for vcruntime140.dll to reduce false positives.

Associated Analytic Story

• APT29 Diplomatic Deceptions with WINELOADER

Risk Based Analytics (RBA)

References

• https://www.mandiant.com/resources/blog/apt29-wineloader-german-political-parties

• https://www.zscaler.com/blogs/security-research/european-diplomats-targeted-spikedwine-wineloader

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