Hacking an SQL-Server

Basically if you’re admin you own everything.

So how would you access an SQL-Server if you don’t have SQL-Permissions but you’re administrator on the system the SQL-server is running on?

Basically you can abuse the fact, that the sql-server has to have at least one account with the necessary permissions. Often this is the local system user.

  1. So just become system using psexec (or anything else): psexec -s cmd.exe
  2. Search for your local SQL-Instance: osql -L
  3. Connect to your SQL-Server using your current (system) credentials: osql -S <InstanceName> -E
  4. If the connection is successful, just enable the sa account and set a new password for it. After that you can use the SQL-Management Studio to administer all permissions:
    /* Enable SQL-User authentication and set sa password */
    ALTER LOGIN sa ENABLE;
    GO
    /* Reset the password, requires CONTROL SERVER permission */
    ALTER LOGIN sa WITH PASSWORD = '<newPassword>';
    GO
    /* just set sa password (alternative way)*/
    sp_password NULL, '<newPassword>', 'sa';
    GO
    
    /* To add an windows user to the admins role do this */
    CREATE LOGIN [DOMAIN\USER] FROM WINDOWS;
    GO
    EXEC sp_addsrvrolemember 'DOMAIN\USER', 'sysadmin';
    GO
    

    If the above is throwing an access denied error for you try a different user for example the mssql service user use process hacker to run a cmd prompt in the context of that user and try again. If also that fails, check if there is any application accessing the database that could have an account with too much permissions e. g. Server Admin instead of db_owner and try that one.

  5. If that all does not help, you have one last way of getting into the database, but that causes a downtime.
  6. Stop your SQL-Server Services (Server, Browser, Agent, …) and open an elevated cmd.
  7. Navigate to the folder containing the executable of the service and start it with the parameter “-m” for single user mode without authentication. After the server is back up do Step 4 and after that stop the server and restart the services you stopped earlier.

WARNING: BY DOING STEP 7 EVERYBODY COULD GAIN FULL ACCESS TO YOUR SERVER, DEPENDING ON YOUR INFRASTRUCTURE YOU MAY WANT TO BLOCK REMOTE CONNECTIONS ON THE WINDOWS FIREWALL WHILE PERFORMING THIS STEP

3 thoughts on “Hacking an SQL-Server”

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