What Is Security
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What Is Security

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What Is Security - DPUG September 2008

What Is Security - DPUG September 2008

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What Is Security What Is Security Presentation Transcript

  • What is Security? DPUG - September 9th 2008 Jason Ragsdale Wednesday, September 10, 2008 1
  • A good place to start... php.ini display_errors = Off register_globals = Off open_basedir = .... What about safe_mode?? Wednesday, September 10, 2008 2
  • Don’t be stupid Never require/include any file based on user input without checking it first. <?php if (isset($_GET[‘page’]) { require $_GET[‘page’]; } ?> URL: script.php?page=/etc/passwd .... nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false root:*:0:0:System Administrator:/var/root:/bin/sh Wednesday, September 10, 2008 3
  • Don’t be stupid... 2 If your solution uses eval().... you are doing it wrong <?php if (isset($_GET[‘input’]) { eval($_GET[‘input’]); } ?> URL: script.php?input=passthru(“cat /etc/passwd”); .... nobody:*:-2:-2:Unprivileged User:/var/empty:/usr/bin/false root:*:0:0:System Administrator:/var/root:/bin/sh Wednesday, September 10, 2008 4
  • Input Filtering What is input? Anything the user or interacting system sends to your site i.e. ($_POST, $_GET, $_REQUEST, $_COOKIE...) What is a whitelist? “A list of approved or favored items” What is a blacklist? “A list persons who are disapproved of or are to be punished or boycotted” Wednesday, September 10, 2008 5
  • Input Validation Unfiltered code Example <?php if (isset($_POST[‘username’])) { $username = $_POST[‘username’]; } Wednesday, September 10, 2008 6
  • Input Validation ctype Example <?php $clean = array(); if (ctype_alnum($_POST[‘username’])) { $clean[‘username’] = $_POST[‘username’]; } Wednesday, September 10, 2008 7
  • Input Validation Zend_Filter_Input Example <?php if (isset($_POST[‘username’])) { $filterChain = new Zend_Filter(); $filterChain->addFilter(new Zend_Filter_Alpha()) ->addFilter(new Zend_Filter_StringToLower()); $username = $filterChain->filter($_POST[‘username’]); } Wednesday, September 10, 2008 8
  • Input Validation php/filter Example <?php if (isset($_POST[‘username’])) { $username = filter_var(‘username’, FILTER_VALIDATE_REGEXP, array( ‘options’=> array(‘regexp’=>’/([a-zA-Z0-9]+)/’) ) ); } Wednesday, September 10, 2008 9
  • Output Encoding What is output? Anything sent back to the user / sender of the request (RSS Feed, Form Validate, User created data...) htmlentities Example <?php $str = “A ‘quote’ is <b>bold</b>”; //Outputs: A ‘quote’ is &lt;b&gt;bold&lt;/b&gt echo htmlentities($str); //Outputs: A &#039;quote&#039; is &lt;b&gt;bold&lt;/b&gt echo htmlentities($str, ENT_QUOTES); Wednesday, September 10, 2008 10
  • Tim Stiles At this point mention XmlWriter and all it’s wonders.... ;) Wednesday, September 10, 2008 11
  • Database Inputs (or: How I Learned to Stop Worrying and Love the Users) Wednesday, September 10, 2008 12
  • How do i deal with it? A input filter (whitelist) combined with prepared statements... DONE $clean = array(); if (ctype_alnum($_POST[‘username’])) { $clean[‘username’] = $_POST[‘username’]; } $sql = “SELECT `username` FROM `users` WHERE `username` = :username”; $sth = $dbh->prepare($sql); $sth->execute(array(‘:username’=> $clean[‘username’])); $username = $sth->fetchColumn(); Wednesday, September 10, 2008 13
  • XSS (Cross Site Scripting) Example <?php echo “<p> Welcome back, {$_GET[‘username’]}.</p>”; ?> ------ Let’s exploit this ------ <p> Welcome back, <script> ....do something bad here... </script>. </p> Wednesday, September 10, 2008 14
  • XSS (Cross Site Scripting) If you do the two items we spoke about Input Filtering Output Encoding You most likely are still vulnerable, but it’ll be a lot harder to exploit Almost impossible to completely nullify all security / XSS stuff (new browsers and plugins all the time + bad guys keep getting smarter) Wednesday, September 10, 2008 15
  • CSRF (Cross Site Request Forgeries) Somewhere on MyFavoriteForum.com: <img src=”bank.com/transfermoney.php? to=me&amount=100.00”> ...if users are logged in, invisible actions can be taken on their behalf, with their authority. Wednesday, September 10, 2008 16
  • CSRF (Cross Site Request Forgeries) Solutions Sign your forms with a token (MD5 hash with a secret key) Validate the token before processing the data This can be done with Cookie and Session data as well Wednesday, September 10, 2008 17
  • Protecting Source Code Make sure all code file extensions are blocked from viewing You can remove them from the html root Or block them in the apache config <FilesMatch “.inc$”> order deny, allow deny from all </FilesMatch> Wednesday, September 10, 2008 18
  • Protecting Source Code Watch for editor backup files too! .file.php.tmp file.php~ etc... Or don’t edit code on production boxes. Wednesday, September 10, 2008 19
  • Code Auditing Set a standard for your team (and yes a team can be a single person) Input Filtering Methods Output Encoding Methods Database Access Methods Search code security points (echo, print...) Enforce these methods Wednesday, September 10, 2008 20
  • Code Auditing Default to Secure. Make being unsecure obvious and auditable YAHOO_GET_RAW( “blah” ) Wednesday, September 10, 2008 21
  • System Security Your website is only as secure as the server/network is it hosted on Perform regular package updates Make sure you apply any updated PHP or Apache code as soon as you can, there are reasons for security releases Wednesday, September 10, 2008 22
  • Firewalls & Access Control Only allow access to ports that you need to 80 - Web 443 - SSL 22 - SSH Wednesday, September 10, 2008 23
  • Misc... Signed Data (MD5) Encrypted passwords in the DB Config Files outside DOCROOT Secret keys outside code, in config files If it’s customer data USE SSL Wednesday, September 10, 2008 24
  • Q&A Wednesday, September 10, 2008 25