1. Web Trust Boundaries and Security Vulnerabilities Haris Volos and Hidayat Teonadi CS739 – Distributed Systems

2. 2 Problem Web of Trust –Web crosses many trust boundaries To avoid Careless Delegation of Trust should follow principles: –Be specific Who is in your trusted group? What actions do we trust them to take? –Be careful Bad design example –A server offloads work to a client that “trusts”, but client is either malicious or is bypassed.

3. 3 Starting point...Java Applets Hypothesis –Applets perform computation on client browser on behalf of the server. Using a web crawler (Larbin), we sought for Java applets. –Besides Java chat applications, other results seem uninteresting. Conclusion –Applets usage is not rampant.

4. 4 Web Apps & JavaScript Interactive Web Applications –Main app resides in server-side (Servlet) –Use JavaScript for client-side computation Example: input data validation Robust Web Applications –JavaScript can be easily circumvented. Can be just disabled by browsers. –Never rely solely on JavaScript client-side validation.

5. 5 Security Vulnerabilities Prevalent, because web apps cross trust boundaries A malicious user will try to exploit these Web app must protect itself –Is cryptography enough? No! –Must validate any data that crosses the trust boundary Example Vulnerabilities –Cross site scripting, SQL Injection

6. 6 Case Study: RoundCube Webmail RoundCube Webmail is a browser based IMAP client. Uses a backend Apache/PHP/MySQL. RSnake from ha.ckers.org exposed a type 1 cross site scripting (XSS) vulnerability –Type-1 XSS: allows foreign code injection into a server generated dynamic page. –Exploit scenario: malicious script can silently obtain sensitive credentials in the form of cookies. We managed to reproduce the XSS vulnerability locally. Realized how seemingly adequate server-side validation can still be circumvented.

7. 7 Next Step Study trust boundary more broadly Find more web applications Use a Web Vulnerability Scanner (e.g. Gamja) to guide search –Expose vulnerabilities –Study them, and –Propose some corrections