Windows Remote Access Software BRC4 Loaded Dll
The following anomaly detection identifies the behavior related to 4 native Windows DLLs being loaded by a non-standard process. Identified by MDSec during their research into Brute Ratel, MDSec identified a high signal analytic by calling out these 4 DLLs being loaded into a process. LogonCLI.dll is the Net Logon Client DLL and is related to users and other domain services to get authenticated. Credui.dll is Credential Manager User Interface. Credential managers receive notifications when authentication information changes. For example, credential managers are notified when a user logs on or an account password changes. Samcli.dll is the Security Accounts Manager Client DLL. Adversaries may attempt to extract credential material from the Security Account Manager (SAM) database either through in-memory techniques or through the Windows Registry where the SAM database is stored. Dbghelp.dll is Windows Image Helper. Windows Image Helper is commonly seen in credential dumping due to native functions. All of these modules are important to monitor and track and combined may lead to credentail access or dumping.
- Type: Anomaly
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2022-08-24
- Author: Teoderick Contreras, Splunk
- ID: 73cf5dcb-cf36-4167-8bbe-384fe5384d05
Kill Chain Phase
- Command and Control
- CIS 10
1 2 3 4 5 6 7 8 9 `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 Computer 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`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
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
|9.0||30||30||a process $Image$ loaded several modules $ImageLoaded$ that might related to credential access on $Computer$.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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