Detection rules › Splunk
DLL Called with Uncommon Function (Windows Event Log)
DLLs can invoke a variety of functions when executed. While these functions are part of legitimate Windows operations, their execution from a DLL file, especially in an unusual context, can be indicative of malicious behavior. Threat actors including Qbot have been observed abusing this technique when calling DLLs with rundll32.exe. This use case detects calls of uncommon functions from DLL files, accounting for instances where rundll32.exe has been renamed. While these function calls may be legitimate, unexpected executions should be investigated
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Stealth | T1218.011 System Binary Proxy Execution: Rundll32 |
References
Event coverage
| Provider | Event | Title |
|---|---|---|
| Security-Auditing | Event ID 4688 | A new process has been created. |
Rule body yaml
id: '27059.49379'
title: DLL Called with Uncommon Function
description: DLLs can invoke a variety of functions when executed. While these functions
are part of legitimate Windows operations, their execution from a DLL file, especially
in an unusual context, can be indicative of malicious behavior. Threat actors including
Qbot have been observed abusing this technique when calling DLLs with rundll32.exe.
This use case detects calls of uncommon functions from DLL files, accounting for
instances where rundll32.exe has been renamed. While these function calls may be
legitimate, unexpected executions should be investigated. Living Off the Land Binary
and Scripts (LOLBAS) (LOLBIN)
logic_format: Splunk
logic: '`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR
"<EventID>4688<" OR Type=Process) ".dll" ("RS32" OR "VirtualAllocEx" OR "NtUnmapViewOfSection"
OR "CreateRemoteThread" OR "RtlCreateUserThread" OR "DeviceIoControl" OR "WriteProcessMemory"
OR "CryptEncrypt" OR "CryptDecrypt" OR "RegSetValueEx" OR "SetWindowsHookEx" OR
"DLLRegisterServer") | rex field=process "\.dll,(?<called_function>[^\s]+)"| where
match(process, "(?i)\.dll\,(RS32|VirtualAllocEx|NtUnmapViewOfSection|CreateRemoteThread|RtlCreateUserThread|DeviceIoControl|WriteProcessMemory|CryptEncrypt|CryptDecrypt|RegSetValueEx|SetWindowsHookEx|DLLRegisterServer)")
| table _time, host, user, process, process_*, parent_process, parent_process_*,
called_function | bin span=1s | stats values(*) as * by _time, host '
techniques:
- defense-evasion:system binary proxy execution:rundll32
technique_id:
- T1218.011
data_category:
- Process command-line parameters
- Windows event logs
references:
- https://redcanary.com/blog/lolbins-abuse/
Stages and Predicates
Stage 1: search
`get_endpoint_data` `get_endpoint_data_winevent` (TERM(EventCode=4688) OR "<EventID>4688<" OR Type=Process) ".dll" ("RS32" OR "VirtualAllocEx" OR "NtUnmapViewOfSection" OR "CreateRemoteThread" OR "RtlCreateUserThread" OR "DeviceIoControl" OR "WriteProcessMemory" OR "CryptEncrypt" OR "CryptDecrypt" OR "RegSetValueEx" OR "SetWindowsHookEx" OR "DLLRegisterServer")
Stage 2: rex
| rex field=process "\.dll,(?<called_function>[^\s]+)"
Stage 3: where
| where match(process, "(?i)\.dll\,(RS32|VirtualAllocEx|NtUnmapViewOfSection|CreateRemoteThread|RtlCreateUserThread|DeviceIoControl|WriteProcessMemory|CryptEncrypt|CryptDecrypt|RegSetValueEx|SetWindowsHookEx|DLLRegisterServer)")
Stage 4: table
| table _time, host, user, process, process_*, parent_process, parent_process_*, called_function
Stage 5: bucket
| bin span=1s
Stage 6: stats
| stats values(*) as * by _time, host
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | TERM |
| 1 | "<EventID>4688<" |
| 1 | ".dll" |
| 1 | "RS32" |
| 1 | "VirtualAllocEx" |
| 1 | "NtUnmapViewOfSection" |
| 1 | "CreateRemoteThread" |
| 1 | "RtlCreateUserThread" |
| 1 | "DeviceIoControl" |
| 1 | "WriteProcessMemory" |
| 1 | "CryptEncrypt" |
| 1 | "CryptDecrypt" |
| 1 | "RegSetValueEx" |
| 1 | "SetWindowsHookEx" |
| 1 | "DLLRegisterServer" |