MSSQL

Microsoft SQL (MSSQL) is Microsoft’s SQL-based relational database management system. Unlike MySQL, which we discussed in the last section, MSSQL is closed source and was initially written to run on Windows operating systems. It is popular among database administrators and developers when building applications that run on Microsoft’s .NET framework due to its strong native support for .NET. There are versions of MSSQL that will run on Linux and MacOS, but we will more likely come across MSSQL instances on targets running Windows.

MSSQL Clients

SQL Server Management Studio (SSMS) comes as a feature that can be installed with the MSSQL install package or can be downloaded & installed separately. It is commonly installed on the server for initial configuration and long-term management of databases by admins. Keep in mind that since SSMS is a client-side application, it can be installed and used on any system an admin or developer is planning to manage the database from. It doesn’t only exist on the server hosting the database. This means we could come across a vulnerable system with SSMS with saved credentials that allow us to connect to the database.

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

• mssql-cli: Command-line interface for MSSQL
• SQL Server PowerShell: PowerShell module for managing SQL Server
• HeidiSQL: Cross-platform database management tool
• SQLPro: Database management tool for MacOS
• Impacket’s mssqlclient.py: Python-based MSSQL client

Of the MSSQL clients listed above, pentesters may find Impacket’s mssqlclient.py to be the most useful due to SecureAuthCorp’s Impacket project being present on many pentesting distributions at install. To find if and where the client is located on our host, we can use the following command:

rnemeth@htb[/htb]$ locate mssqlclient

/usr/bin/impacket-mssqlclient
/usr/share/doc/python3-impacket/examples/mssqlclient.py

MSSQL Databases

MSSQL has default system databases that can help us understand the structure of all the databases that may be hosted on a target server. Here are the default databases and a brief description of each:

Table source: System Databases Microsoft Doc

Default Configuration

When an admin initially installs and configures MSSQL to be network accessible, the SQL service will likely run as NT SERVICE\MSSQLSERVER. Connecting from the client-side is possible through Windows Authentication, and by default, encryption is not enforced when attempting to connect.

Authentication being set to Windows Authentication means that the underlying Windows OS will process the login request and use either the local SAM database or the domain controller (hosting Active Directory) before allowing connectivity to the database management system. Using Active Directory can be ideal for auditing activity and controlling access in a Windows environment, but if an account is compromised, it could lead to privilege escalation and lateral movement across a Windows domain environment. Like with any OS, service, server role, or application, it can be beneficial to set it up in a VM from installation to configuration to understand all the default configurations and potential mistakes that the administrator could make.

Dangerous Settings

It can be beneficial to place ourselves in the perspective of an IT administrator when we are on an engagement. This mindset can help us remember to look for various settings that may have been misconfigured or configured in a dangerous manner by an admin. A workday in IT can be rather busy, with lots of different projects happening simultaneously and the pressure to perform with speed & accuracy being a reality in many organizations, mistakes can be easily made. It only takes one tiny misconfiguration that could compromise a critical server or service on the network. This applies to just about every network service and server role that can be configured, including MSSQL.

This is not an extensive list because there are countless ways MSSQL databases can be configured by admins based on the needs of their respective organizations. We may benefit from looking into the following:

Footprinting the Service

There are many ways we can approach footprinting the MSSQL service, the more specific we can get with our scans, the more useful information we will be able to gather. NMAP has default mssql scripts that can be used to target the default tcp port 1433 that MSSQL listens on.

NMAP MSSQL Script Scan

The scripted NMAP scan below provides us with helpful information. We can see the hostname, database instance name, software version of MSSQL and named pipes are enabled. We will benefit from adding these discoveries to our notes.

rnemeth@htb[/htb]$ 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

Starting Nmap 7.91 ( https://nmap.org ) at 2021-11-08 09:40 EST
Nmap scan report for 10.129.201.248
Host is up (0.15s latency).

PORT     STATE SERVICE  VERSION
1433/tcp open  ms-sql-s Microsoft SQL Server 2019 15.00.2000.00; RTM
| ms-sql-ntlm-info: 
|   Target_Name: SQL-01
|   NetBIOS_Domain_Name: SQL-01
|   NetBIOS_Computer_Name: SQL-01
|   DNS_Domain_Name: SQL-01
|   DNS_Computer_Name: SQL-01
|_  Product_Version: 10.0.17763

Host script results:
| ms-sql-dac: 
|_  Instance: MSSQLSERVER; DAC port: 1434 (connection failed)
| ms-sql-info: 
|   Windows server name: SQL-01
|   10.129.201.248\MSSQLSERVER: 
|     Instance name: MSSQLSERVER
|     Version: 
|       name: Microsoft SQL Server 2019 RTM
|       number: 15.00.2000.00
|       Product: Microsoft SQL Server 2019
|       Service pack level: RTM
|       Post-SP patches applied: false
|     TCP port: 1433
|     Named pipe: \\10.129.201.248\pipe\sql\query
|_    Clustered: false

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 8.52 seconds

MSSQL Ping in Metasploit

We can also use Metasploit to run an auxiliary scanner called mssql_ping that will scan the MSSQL service and provide helpful information in our footprinting process.

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

rhosts => 10.129.201.248


msf6 auxiliary(scanner/mssql/mssql_ping) > run

[*] 10.129.201.248:       - SQL Server information for 10.129.201.248:
[+] 10.129.201.248:       -    ServerName      = SQL-01
[+] 10.129.201.248:       -    InstanceName    = MSSQLSERVER
[+] 10.129.201.248:       -    IsClustered     = No
[+] 10.129.201.248:       -    Version         = 15.0.2000.5
[+] 10.129.201.248:       -    tcp             = 1433
[+] 10.129.201.248:       -    np              = \\SQL-01\pipe\sql\query
[*] 10.129.201.248:       - Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed

Connecting with mssqlclient.py

If we can guess or gain access to credentials, this allows us to remotely connect to the MSSQL server and start interacting with databases using T-SQL (Transact-SQL). Authenticating with MSSQL will enable us to interact directly with databases through the SQL Database Engine. From Pwnbox or a personal attack host, we can use Impacket’s mssqlclient.py to connect as seen in the output below. Once connected to the server, it may be good to get a lay of the land and list the databases present on the system.

rnemeth@htb[/htb]$ python3 mssqlclient.py Administrator@10.129.201.248 -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                                                                                                                               

--------------------------------------------------------------------------------------

master                                                                                                                             

tempdb                                                                                                                             

model                                                                                                                              

msdb                                                                                                                               

Transactions    

Security Best Practices

When setting up an MSSQL server, it is important to follow security best practices:

• Strong credentials: Use strong passwords for MSSQL users, especially the sa account. Consider disabling the sa account if not needed
• Encryption: Enable encryption for connections to prevent data interception
• Certificate management: Use properly signed certificates instead of self-signed certificates
• Windows Authentication: Leverage Windows Authentication for better integration with Active Directory and centralized access control
• Network access: Restrict network access to MSSQL servers; avoid exposing them to public networks unless necessary
• Named pipes: Disable named pipes if not required for your environment
• Principle of least privilege: Follow the principle of least privilege when granting user permissions
• Regular updates: Keep MSSQL server updated with the latest security patches
• Audit logging: Enable audit logging to track database access and changes