Adversaries may abuse Regsvr32.exe to proxy execution of malicious code. Regsvr32.exe is a command-line program used to register and unregister object linking and embedding controls, including dynamic link libraries (DLLs), on Windows systems. The Regsvr32.exe binary may also be signed by Microsoft. [1]
Malicious usage of Regsvr32.exe may avoid triggering security tools that may not monitor execution of, and modules loaded by, the regsvr32.exe process because of allowlists or false positives from Windows using regsvr32.exe for normal operations. Regsvr32.exe can also be used to specifically bypass application control using functionality to load COM scriptlets to execute DLLs under user permissions. Since Regsvr32.exe is network and proxy aware, the scripts can be loaded by passing a uniform resource locator (URL) to file on an external Web server as an argument during invocation. This method makes no changes to the Registry as the COM object is not actually registered, only executed. [2] This variation of the technique is often referred to as a "Squiblydoo" and has been used in campaigns targeting governments. [3] [4]
Regsvr32.exe can also be leveraged to register a COM Object used to establish persistence via Component Object Model Hijacking. [3]
| ID | Name | Description |
|---|---|---|
| S0622 | AppleSeed | |
| G0073 | APT19 |
APT19 used Regsvr32 to bypass application control techniques.[6] |
| G0050 | APT32 |
APT32 created a Scheduled Task/Job that used regsvr32.exe to execute a COM scriptlet that dynamically downloaded a backdoor and injected it into memory. The group has also used regsvr32 to run their backdoor.[7][8][9] |
| S0373 | Astaroth | |
| G0108 | Blue Mockingbird |
Blue Mockingbird has executed custom-compiled XMRIG miner DLLs using regsvr32.exe.[11] |
| C0015 | C0015 |
During C0015, the threat actors employed code that used |
| G0080 | Cobalt Group |
Cobalt Group has used regsvr32.exe to execute scripts.[13][14][15] |
| S1155 | Covenant |
Covenant can create SCT files for installation via |
| G0009 | Deep Panda |
Deep Panda has used regsvr32.exe to execute a server variant of Derusbi in victim networks.[17] |
| S0021 | Derusbi |
Derusbi variants have been seen that use Registry persistence to proxy execution through regsvr32.exe.[18] |
| S0384 | Dridex | |
| S0554 | Egregor |
Egregor has used regsvr32.exe to execute malicious DLLs.[20] |
| S0367 | Emotet | |
| S0568 | EVILNUM |
EVILNUM can run a remote scriptlet that drops a file and executes it via regsvr32.exe.[22] |
| S0698 | HermeticWizard |
HermeticWizard has used |
| S0087 | Hi-Zor |
Hi-Zor executes using regsvr32.exe called from the Registry Run Keys / Startup Folder persistence mechanism.[24] |
| G0100 | Inception |
Inception has ensured persistence at system boot by setting the value |
| G0094 | Kimsuky | |
| S0250 | Koadic | |
| G0065 | Leviathan | |
| S0284 | More_eggs |
More_eggs has used regsvr32.exe to execute the malicious DLL.[29] |
| S1047 | Mori | |
| C0022 | Operation Dream Job |
During Operation Dream Job, Lazarus Group used |
| S0229 | Orz |
Some Orz versions have an embedded DLL known as MockDll that uses Process Hollowing and regsvr32 to execute another payload.[28] |
| S0650 | QakBot |
QakBot can use Regsvr32 to execute malicious DLLs.[32][33][34][35][36][37] |
| S0481 | Ragnar Locker |
Ragnar Locker has used regsvr32.exe to execute components of VirtualBox.[38] |
| S1130 | Raspberry Robin |
Raspberry Robin uses regsvr32.exe execution without any command line parameters for command and control requests to IP addresses associated with Tor nodes.[39] |
| S0270 | RogueRobin |
RogueRobin uses regsvr32.exe to run a .sct file for execution.[40] |
| S1018 | Saint Bot | |
| S1030 | Squirrelwaffle |
Squirrelwaffle has been executed using |
| G0127 | TA551 | |
| S0476 | Valak |
Valak has used |
| G0090 | WIRTE |
WIRTE has used |
| S0341 | Xbash |
| ID | Mitigation | Description |
|---|---|---|
| M1050 | Exploit Protection |
Microsoft's Enhanced Mitigation Experience Toolkit (EMET) Attack Surface Reduction (ASR) feature can be used to block regsvr32.exe from being used to bypass application control. [48] Identify and block potentially malicious software executed through regsvr32 functionality by using application control [49] tools, like Windows Defender Application Control[50], AppLocker, [51] [52] or Software Restriction Policies [53] where appropriate. [54] |
| ID | Data Source | Data Component | Detects |
|---|---|---|---|
| DS0017 | Command | Command Execution |
Command arguments used before and after the regsvr32.exe invocation may also be useful in determining the origin and purpose of the script or DLL being loaded. [3] |
| DS0011 | Module | Module Load |
Monitor DLL/PE file events, specifically creation of these binary files as well as the loading of DLLs into processes. Look for DLLs that are not recognized or not normally loaded into a process. Note: This looks for unsigned images that may be loaded by regsvr32, while attempting to eliminate false positives stemming from Windows/Program Files binaries. Analytic 5 - Loading Unsigned Images
|
| DS0029 | Network Traffic | Network Connection Creation |
Monitor for newly constructed network connections that are sent or received by untrusted hosts. |
| DS0009 | Process | Process Creation |
Use process monitoring to monitor the execution and arguments of regsvr32.exe. Compare recent invocations of regsvr32.exe with prior history of known good arguments and loaded files to determine anomalous and potentially adversarial activity. Note: Event IDs are for Sysmon (Event ID 1 - process create) and Windows Security Log (Event ID 4688 - a new process has been created). - Analytic 1 is a more generic analytic that looks for suspicious usage of regsvr32.exe, specifically for cases where regsvr32.exe creates child processes that aren’t itself. It’s not likely that this will result in millions of hits, but it does occur during benign activity so some form of baselining would be necessary for this to be useful as an alerting analytic.- Analytic 2 is around "Squiblydoo", which is a specific usage of regsvr32.exe to load a COM scriptlet directly from the internet and execute it in a way that bypasses application whitelisting. It looks for regsvr32.exe process creation events that load scrobj.dll via the command-line (which executes the COM scriptlet).- Analytic 3 This uses the same logic as above, but adds lightweight baselining by ignoring all results that also showed up in the previous 30 days (it runs over 1 day).- Analytic 4 This looks for child processes that may be spawend by regsvr32, while attempting to eliminate some of the common false positives such as werfault (Windows Error Reporting). Analytic 1 - Generic Regsvr32
Analytic 2 - Squiblydoo
Analyt 3 - New Items since last month
Analytic 4 - Spawning Child Processes
|