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204 Web Application Penetration Testing /set the token as in the session data $_SESSION[‘antiCsrf’] = $csrfToken; /Transfer form with the hidden field $form = ‘ BANK XYZ - Confirm Transfer Do You want to confirm a transfer of ’. $_REQUEST[‘amount’] .’ € to account: ’. $_RE- QUEST[‘account’] .’ ? a random token generated in the second step and accepting only variable passed via POST method. In this situation an attacker could forge a CSRF + Clickjacking attack to evade anti-CSRF protection and force a victim to do a money transfer without her consent. The target page for the attack is the second step of the money transfer procedure. Since the developers put the security controls only in the last step, thinking that this is secure enough, the attacker could pass the account and amount parameters via GET method. (Note: there is an advanced clickjacking attack that permits to force users to fill a form, so also in the case in which is required to fill a form, the attack is feasible). The attacker’s page may look a simple and harmless web page like the one presented below: But playing with the CSS opacity value we can see what is hidden under a seemingly innocuous web page. ’; In the last step are planned security controls and then, if is all ok, the transfer is done. Following is presented a snippet of the code of the last step (Note: in this example, for simplicity, there is no input sanitization, but it has no relevance to block this type of attack): if( (!empty($_SESSION[‘antiCsrf’])) && (!empty($_POST[‘antiCsrf’])) ) { /here we can suppose input sanitization code… /check the anti-CSRF token if( ($_SESSION[‘antiCsrf’] == $_POST[‘antiCsrf’]) ) { echo ‘ ‘. $_POST[‘amount’] .’ € successfully transfered to account: ‘. $_POST[‘account’] .’ ’; } } else { } echo ‘Transfer KO’; As you can see the code is protected from CSRF attack both with The clickjacking code the create this page is presented below: Trusted web page
205 Web Application Penetration Testing } #content { width: 500px; height: 500px; margin-top: 150px ; margin-left: 500px; } #clickjacking { position: absolute; left: 172px; top: 60px; filter: alpha(opacity=0); } /--> opacity:0.0 Tools • Context Information Security: “Clickjacking Tool” - http://www contextis.com/research/tools/clickjacking-tool/ References OWASP Resources • Clickjacking Whitepapers • Marcus Niemietz: “UI Redressing: Attacks and Countermeasures Revisited” - http://ui-redressing.mniemietz.de/uiRedressing.pdf • “Clickjacking” - https://en.wikipedia.org/wiki/Clickjacking • Gustav Rydstedt, Elie Bursztein, Dan Boneh, and Collin Jackson: “Busting Frame Busting: a Study of Clickjacking Vulnerabilities on Popular Sites” - http://seclab.stanford.edu/websec/framebusting/ framebust.pdf • Paul Stone: “Next generation clickjacking” - https://media.blackhat com/bh-eu-10/presentations/Stone/BlackHat-EU-2010-Stone- Next-Generation-Clickjacking-slides.pdf www.owasp.com With the help of CSS (note the #clickjacking block) we can mask and suitably position the iframe in such a way as to match the buttons. If the victim click on the button “Click and go!” the form is submitted and the transfer is completed. Testing WebSockets (OTG-CLIENT-010) Summary Traditionally the HTTP protocol only allows one request/response per TCP connection. Asynchronous JavaScript and XML (AJAX) allows clients to send and receive data asynchronously (in the background without a page refresh) to the server, however, AJAX requires the client to initiate the requests and wait for the server responses (half-duplex). HTML5 WebSockets allow the client/server to create a ‘full-duplex’ (two-way) communication channels, allowing the client and server to truly communicate asynchronously. WebSockets conduct their initial ‘upgrade’ handshake over HTTP and from then on all communication is carried out over TCP channels by use of frames. Origin It is the server’s responsibility to verify the Origin header in the initial HTTP WebSocket handshake. If the server does not validate the origin header in the initial WebSocket handshake, the WebSocket server may accept connections from any origin. This could allow attackers to communicate with the WebSocket server cross-domain allowing for Top 10 2013-A8-Cross-Site Request Forgery (CSRF) type issues. Confidentiality and Integrity WebSockets can be used over unencrypted TCP or over encrypted TLS. To use unencrypted WebSockets the ws:// URI scheme is used (default port 80), to use encrypted (TLS) WebSockets the wss:// URI scheme is used (default port 443). Look out for Top 10 2013-A6-Sensitive Data Exposure type issues. Authentication WebSockets do not handle authentication, instead normal application authentication mechanisms apply, such as cookies, HTTP Authentication or TLS authentication. Look out for Top 10 2013-A2-Broken Authentication and Session Management type issues. The example presented uses only basic clickjacking technique, but with advanced technique is possible to force user filling form with values defined by the attacker. Authorization WebSockets do not handle authorization, normal application authorization mechanisms apply. Look out for Top 10 2013-A4-Insecure Direct Object References and Top 10 2013-A7-Missing Function Level Access Control type issues.
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