NGSSoftware Insight Security Research Advisory Name: Arbitrary Command Execution on SQL Server 2000 Systems: Microsoft SQL Server 2000 SP 2 Severity: High Risk for Distributor servers Category: Arbitrary Command Execution Vendor URL: http://www.microsoft.com/ Author: David Litchfield (davidat_private) Advisory URL: http://www.ngssoftware.com/advisories/mssql-sp_MScopyscriptfile.txt Date: 22nd August 2002 Advisory number: #NISR22002002A Description *********** A stored procedure on an SQL Server is a series of SQL queries that can be written once and run many times. One of the internal Microsoft stored procedures on SQL Server 2000 that the 'public' role has permissions to execute fails to validate user input before passing it to xp_cmdshell. The xp_cmdshell extended stored procedure runs an operating system command and it is possible for a low privileged and malicious user to insert and run their own arbitrary commands. Details ******* If a Microsoft SQL Server is configured as a distributor, so it can replicate data between servers, a low privileged and malicious user may execute the 'sp_MScopyscript' stored procedure and insert arbitrary commands which will be run in the security context of the SQL Server account. If the SQL Server is running as LocalSytem then this attack will invariably fail. The reasons behind this is due to the fact that, before the user supplied commands are executed, the server must create a directory over a network share on the distributor. As the Local System account has no pivileges on the network, the stored procedure will fail at this point. If the server is running in the context of a domain user then the "make directory" command should work provided replication has been setup properly. Once this command has executed the stored procedure then inserts the user supplied @scriptfile parameter into a command: from the text of sp_MScopyscript select @cmd = N'copy "' + @scriptfile + N'" "' + @directory + N'"' exec @retcode = master..xp_cmdshell @cmd, NO_OUTPUT By supplying a malformed @scriptfile parameter an attacker can run arbitrary commands: use master declare @cmd nvarchar(4000) exec sp_MScopyscriptfile N'c:\autoexec.bat" c:\cp.txt&echo hello > c:\ccc.bbb & echo "hello',@cmd OUTPUT print @cmd The above query will copy the autoexec.bat file to cp.txt but also echo hello to a file called ccc.bbb. If the server is running with Administrator privileges an attacker will be able to insert pretty much any command. For example the could create a Windows NT user and add it to the administrators group. Fix Information *************** The last cumulative patch provided by Microsoft ( see http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/ bulletin/MS02-043.asp ) appears to address this problem. If you have not applied this patch yet NGSSoftware recommend you do so as soon as possible. For those who have to wait to apply the patch due to testing periods etc NGSSoftware recommend that you at least prevent the 'public' role from running this stored procedure. You can do this by running the following query from Query Analyzer: REVOKE EXECUTE ON [dbo].[sp_MScopyscriptfile] FROM [public] CASCADE
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