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A Simple Ransomware Protection

We see ransomware delete all shadow copies usingvssadmin pretty often. What if we could just intercept that request and kill the invoking process? Let's try to create a simple vaccine.

Weregister a debugger forvssadmin.exe (andwmic.exe), which is our compiledraccine.exe. Raccine is a binary, that first collects all PIDs of the parent processes and then tries to kill all parent processes.

Advantages:

• The method is rather generic
• We don't have to replace a system file (vssadmin.exe orwmic.exe), which could lead to integrity problems and could break our raccination on each patch day
• Flexible YARA rule scanning of command line params for malicious activity
• The changes are easy to undo
• Runs on Windows 7 / Windows 2008 R2 or higher
• No running executable or additional service required (agent-less)

Disadvantages / Blind Spots:

• The legitimate use ofvssadmin.exe delete shadows (or any other blacklisted combination) isn't possible anymore
• It even kills the processes that tried to invokevssadmin.exe delete shadows, which could be a backup process
• This won't catch methods in which the malicious process isn't one of the processes in the tree that has invokedvssadmin.exe (e.g. viaschtasks)

1. Invocation ofvssadmin.exe (andwmic.exe) gets intercepted and passed toraccine.exe as debugger (vssadmin.exe delete shadows becomesraccine.exe vssadmin.exe delete shadows)
2. We then process the command line arguments and look for malicious combinations using Yara rules.
3. If no malicious combination could be found, we create a new process with the original command line parameters.
4. If a malicious combination could be found, we collect all PIDs of parent processes and the start killing them (this should be the malware processes as shown in the screenshots above). Raccine shows a command line window with the killed PIDs for 5 seconds, logs it to the Windows Eventlog and then exits itself.

Malicious combinations:

• delete andshadows (vssadmin, diskshadow)
• resize andshadowstorage (vssadmin)
• delete andshadowstorage (vssadmin)
• delete andshadowcopy (wmic)
• delete andcatalog and-quiet (wbadmin)
• win32_shadowcopy or element from a list of encoded commands (powershell)
• recoveryenabled (bcedit)
• ignoreallfailures (bcedit)

^ outdated list: check the correspondingYARA rule

Powershell list of encoded commands:JAB,SQBFAF,SQBuAH,SUVYI,cwBhA,aWV4I,aQBlAHgA and many more

Emotet without Raccine -Link

Emotet with Raccine -Link (ignore the process activity that is related to the Raccine installation)

The infection gets nipped in the bud.

USE IT AT YOUR OWN RISK!

You won't be able to run commands that use the blacklisted commands on a raccinated machine anymore until you apply the uninstall patchraccine-reg-patch-uninstall.reg. This could break various backup solutions that run that specific command during their work. It will not only block that request but kill all processes in that tree including the backup solution and its invoking process.

If you have a solid security monitoring that logs all process executions, you could check your logs to see ifvssadmin.exe delete shadows,vssadmin.exe resize shadowstorage ... or the other blocked command lines are frequently or sporadically used for legitimate purposes in which case you should refrain from using Raccine.

• 0.1.0 - Initial version that intercepted & blocked all vssadmin.exe executions
• 0.2.0 - Version that blocks only vssadmin.exe executions that containdelete andshadows in their command line and otherwise pass all parameters to a new process that invokes vssadmin with its original parameters
• 0.2.1 - Removedexplorer.exe from the whitelist
• 0.3.0 - Supports thewmic method callingdelete shadowcopy, no outputs for whitelisted process starts (avoids problems with wmic output processing)
• 0.4.0 - Supports logging to the Windows Eventlog for each blocked attempt, looks for more malicious parameter combinations
• 0.4.1 - Statically linked binaries
• 0.4.2 - Bugfixes provided by John Lambert
• 0.5.0 - Removed Eventlog logging (basic info was unnecessary; cuased higher complexity; can be achieved by process creation logging as well), support for wbadmin filtering
• 0.5.1 - Improvements by @JohnLaTwC
• 0.5.2 - Additional check fordelete shadowstorage by @JohnLaTwC, code review by @_hillu, application icon
• 0.5.3 - Batch installer
• 0.6.0 - Additional checks forbcdedit.exe /set {default} bootstatuspolicy ignoreallfailures andbcdedit.exe /set {default} recoveryenabled no
• 0.7.0 - Additional checks forpowershell.exe andwin32_shadowcopy or a list of encoded commands
• 0.7.1 - Improvements by @JohnLaTwC
• 0.7.2 - Using absolute paths in registry patches
• 0.8.0 - Creates a log file with all intercepted requests and actions performedC:\ProgramData\Raccine_log.txt
• 0.9.0 - Logs to Windows Eventlog by @JohnLaTwC
• 0.10.0 - Simulation mode only
• 0.10.1 - Fix for Simulation mode
• 0.10.2 - Includesdiskshadow.exe delete shadows command
• 0.10.3-5 - Minor fixes and additions
• 1.0 BETA - GUI elements and YARA rule scanning of command line params
• 1.1 BETA - YARA rule matching with external variables, troubleshooting functions
• 1.2 BETA - Signature Updater
• 1.3 BETA - In-Memory YARA Scanning of invoking parent process
• 1.4 BETA - Full x86 support, moved static strings to YARA rules to avoid AV detections, Log of accepted executions, .NET Framework setup in installer
• 1.4.2 BETA - Exit code fix (pass through of exit code returned by the intercepted program), intercept taskkill.exe

• VC++ Runtime for YARA scanning (Installer contains the setup package fromhttps://aka.ms/vs/16/release/VC_redist.x64.exe)
• .NET Framework 4.5
• Internet access for the YARA rule updates
• Windows 7 / Windows 2008 R2 or higher

Both the Visual C++ Redistributable package and the .NET Framework will be automatically installed runninginstall-raccine.bat.

1. DownloadRaccine.zip from theRelease section
2. Extract it
3. Runraccine-installer.bat as administrator

The batch installer includes an "uninstall" option.

As Administrator do:

1. Runraccine-reg-patch-uninstall.reg
2. Remove%ProgramFiles%\Raccine and%ProgramData%\Raccine folders
3. Runreg delete HKCU\Software\Raccine /F
4. Runtaskkill /F /IM RaccineSettings.exe
5. Runreg delete "HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /V "Raccine Tray" /F
6. Runschtasks /DELETE /TN "Raccine Rules Updater" /F

We recommend an uninstall and reinstall to upgrade. An uninstall removes all registry keys with configurations.

Raccine has an integrated signature-updater since version 1.2. This program namedRaccineRulesSync.exe is configured to run once a day via scheduled task. You can run a signature update manually using the option in the tray icon menu.

Since version 1.0, Raccine additionally uses YARA rules to determine if a process command line or parent process is malicious or not. Raccine uses 2 sets of rules for two different purposes.

1. ./yara - rules that get applied to the command line with all parameters, e.g.WMIC.exe delete justatest
2. ./yara/in-memory - rules that get applied to process memory of the parent process of our intercepted process, e.g. ransomware.exe running our intercepted process vssadmin.exe

Since version 1.1 we pass a list of external variables into the YARA matching process to allow for much more complex and clever YARA rules that take attributes of the process and its parent into account.

The matching process looks like this on the command line:

"C:\Program Files\Raccine\yara64.exe" -d FromRaccine="true" -d Name="WMIC.exe" -d ExecutablePath="C:\Windows\System32\wbem\WMIC.exe" -d CommandLine="WMIC.exe delete justatest" -d  Priority=32 -d FromRaccine="true" -d ParentName="cmd.exe" -d ParentExecutablePath="C:\Windows\System32\cmd.exe" -d ParentCommandLine="'C:\WINDOWS\system32\cmd.exe'" -d ParentPriority=32 C:\ProgramData\Raccine\yarayara\mal_emotet.yar C:\ProgramData\Raccine\yara\Rac1C6A.tmp

The following listing shows an example YARA rule that makes use of the external variables in its condition.

ruleenv_vars_test{    condition:Namecontains"WMIC.exe"andCommandLinecontains"delete justatest"andParentPriority>=8and(ParentCommandLinecontains"cmd"orParentCommandLinecontains"powershell")}

The folderGPO includesRaccine.ADMX andRaccine.ADML. In deployment theRaccine.ADMX file goes inC:\Windows\PolicyDefinitions. The accompanyingRaccine.ADML files goes inC:\Windows\PolicyDefinitions\en-US.

To use: OpenGPEDIT.MSC > Computer Configuration > Administrative Templates > System > Raccine

After configuring the changes, you may need to bump gpo by runninggpupdate.exe.

A logfile with all interceptions and actions taken is written toC:\ProgramData\Raccine\Raccine_log.txt

An entry is generated by every blocking event in theApplication eventlog.

The IDs that Raccine generates

• EventId 1 - Setup activity
• EventId 2 - Malicious activity detected
• EventId 3 - Benign activity detected

Since version 0.10.0, Raccine can be installed in "simulation mode", which activates all triggers, logs all actions but doesn't kill anything. This mode should be used in environments in which backup solutions or other legitimate software for a reasonable amount of time to check if Raccine would interfere with other software. The idea is to install Raccine in simulation mode, let it log for a week or month and then check the logs to see if it would have blocked legitimate software used in the organisation.

Runraccine.exe and watch the parent process tree die (screenshot of v0.1)

Available and required since version 1.

In case that the Ransomware that your're currently handling uses a certain process name, e.g.taskdl.exe, you could just change the.reg patch to intercept calls to that name and let Raccine kill all parent processes of the invoking process tree.

I'd like to extend Raccine but lack the C++ coding skills, especially on the Windows platform.

If anything happens to your installation, e.g. sudden error messages, broken services or programs that won't start anymore, run the fileraccine-reg-patch-uninstall.reg in thereg-patches sub folder. This should bring everything back to normal.

After that your should also be able to run a full uninstallation usinginstall-raccine.bat.

The right pronounciation is "Rax-Een".

• Florian Roth@cyb3rops
• John Lambert@JohnLaTwC
• Eran Yom-Tov@eran_yom_tov
• Ollie Whitehouse@ollieatnccgroup
• Branislav Đalić@LordOfThePies4
• Hilko Bengen@hillu