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.

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 icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows_unsigned_ms_dll_side_loading_filter search *
windows_unsigned_ms_dll_side_loading_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1574.002 DLL Side-Loading Defense Evasion
T1547 Boot or Logon Autostart Execution Persistence
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_AE
Cis18Value.CIS_10
APT19
APT3
APT32
APT41
BRONZE BUTLER
BlackTech
Chimera
Cinnamon Tempest
Daggerfly
Earth Lusca
FIN13
GALLIUM
Higaisa
Lazarus Group
LuminousMoth
MuddyWater
Mustang Panda
Naikon
Patchwork
SideCopy
Sidewinder
Threat Group-3390
Tropic Trooper
menuPass

Default Configuration

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

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

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

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
An instance of $Image$ loading Unsigned $ImageLoaded$ was detected on $dest$. 9 30 30
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Passing N/A N/A N/A
Unit Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

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