Detection: Windows Unsigned DLL Side-Loading

Description

The following analytic detects the creation of potentially malicious unsigned DLLs in the c:\windows\system32 or c:\windows\syswow64 folders. It leverages Sysmon EventCode 7 logs to identify unsigned DLLs with unavailable signatures loaded in these critical directories. This activity is significant as it may indicate a DLL hijacking attempt, a technique used by attackers to gain unauthorized access and execute malicious code. If confirmed malicious, this could lead to privilege escalation, allowing the attacker to gain elevated privileges and further compromise the target system.

1`sysmon` EventCode=7 Signed=false OriginalFileName = "-" SignatureStatus="unavailable" ImageLoaded IN ("*:\\windows\\system32\\*", "*:\\windows\\syswow64\\*") 
2| stats count min(_time) as firstTime max(_time) as lastTime by Image ImageLoaded Signed SignatureStatus OriginalFileName process_name dest EventCode ProcessId Hashes IMPHASH 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_unsigned_dll_side_loading_filter`

Data Source

Name Platform Sourcetype Source Supported App
Sysmon EventID 7 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' N/A

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
windows_unsigned_dll_side_loading_filter search *
windows_unsigned_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
KillChainPhase.EXPLOITAITON
KillChainPhase.INSTALLATION
NistCategory.DE_AE
Cis18Value.CIS_10
APT19
APT3
APT32
APT41
BRONZE BUTLER
BlackTech
Chimera
Cinnamon Tempest
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

To successfully implement this search, you need to be ingesting logs with the process name and imageloaded executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

It is possible some Administrative utilities will load dismcore.dll outside of normal system paths, filter as needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
An unsigned dll module was loaded on $dest$ 49 70 70
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: 2