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Description

The following analytic identifies the loading of four specific Windows DLLs (credui.dll, dbghelp.dll, samcli.dll, winhttp.dll) by a non-standard process. This detection leverages Sysmon EventCode 7 to monitor DLL load events and flags when all four DLLs are loaded within a short time frame. This activity is significant as it may indicate the presence of Brute Ratel C4, a sophisticated remote access tool used for credential dumping and other malicious activities. If confirmed malicious, this behavior could lead to unauthorized access, credential theft, and further compromise of the affected system.

  • Type: Anomaly

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-05-21
  • Author: Teoderick Contreras, Splunk
  • ID: 73cf5dcb-cf36-4167-8bbe-384fe5384d05

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1219 Remote Access Software Command And Control
T1003 OS Credential Dumping Credential Access
Kill Chain Phase
  • Command and Control
  • Exploitation
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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`sysmon` EventCode=7 
|bin _time span=30s 
| eval BRC4_AnomalyLoadedDll=case(OriginalFileName=="credui.dll", 1, OriginalFileName=="DBGHELP.DLL", 1, OriginalFileName=="SAMCLI.DLL", 1, OriginalFileName=="winhttp.dll", 1, 1=1, 0) 
| eval BRC4_LoadedDllPath=case(match(ImageLoaded, "credui.dll"), 1, match(ImageLoaded, "dbghelp.dll"), 1, match(ImageLoaded, "samcli.dll"), 1, match(ImageLoaded, "winhttp.dll"), 1, 1=1, 0) 
| stats count min(_time) as firstTime max(_time) as lastTime values(ImageLoaded) as ImageLoaded values(OriginalFileName) as OriginalFileName dc(ImageLoaded) as ImageLoadedCount by Image  BRC4_LoadedDllPath BRC4_AnomalyLoadedDll dest EventCode Signed 
| where  ImageLoadedCount == 4 AND (BRC4_LoadedDllPath == 1 OR BRC4_AnomalyLoadedDll == 1) 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `windows_remote_access_software_brc4_loaded_dll_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_remote_access_software_brc4_loaded_dll_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
  • Image
  • ImageLoaded
  • process_name
  • dest
  • EventCode
  • Signed
  • ProcessId

How To Implement

The latest Sysmon TA 3.0 https://splunkbase.splunk.com/app/5709 will add the ImageLoaded name to the process_name field, allowing this query to work. Use as an example and implement for other products.

Known False Positives

This module can be loaded by a third party application. Filter is needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
9.0 30 30 a process $Image$ loaded several modules $ImageLoaded$ that might related to credential access on $dest$.

:information_source: 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

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

source | version: 2