Top 10 Web 2.0 Attack Vectors
by Shreeraj Shah - net square - Monday, 9 October 2006.
Web 2.0 is the novel term coined for new generation Web applications. start.com, Google maps, Writely and MySpace.com are a few examples. The shifting technological landscape is the driving force behind these Web 2.0 applications. On the one hand are Web services that are empowering server-side core technology components and on the other hand are AJAX and Rich Internet Application (RIA) clients that are enhancing client-end interfaces in the browser itself.

XML is making a significant impact at both presentation and transport (HTTP/HTTPS) layers. To some extent XML is replacing HTML at the presentation layer while SOAP is becoming the XML-based transport mechanism of choice.

Web 2.0 security concerns – reshaping the industry

This technological transformation is bringing in new security concerns and attack vectors into existence. Yamanner, Samy and Spaceflash type worms are exploiting “client-side” AJAX frameworks, providing new avenues of attack and compromising some of the confidential information.

On the “server-side”, XML based Web services are replacing some of the key functionalities and providing distributed application access through Web services interfaces. These remote capabilities to invoke methods over GET, POST or SOAP from the Web browser itself provide new openings to applications. On other side, RIA frameworks running on XML, XUL, Flash, Applets and JavaScripts are adding new possible sets of vectors. RIA, AJAX and Web services are adding new dimensions to Web application security.

Here is the list of 10 attack vectors along with a brief overview of each:

1. Cross-site scripting in AJAX

In the last few months, several cross-site scripting attacks have been observed, where malicious JavaScript code from a particular Web site gets executed on the victim’s browser thereby compromising information. A recent example is the Yamanner worm that exploited cross-site scripting opportunities in Yahoo mail’s AJAX call. Another recent example is the Samy worm that exploited MySpace.com’s cross-site scripting flaw. AJAX gets executed on the client-side by allowing an incorrectly written script to be exploited by an attacker. The attacker is only required to craft a malicious link to coax unsuspecting users to visit a certain page from their Web browsers. This vulnerability existed in traditional applications as well but AJAX has added a new dimension to it.

2. XML poisoning

XML traffic goes back and forth between server and browser in many of the WEB 2.0 applications. Web applications consume XML blocks coming from AJAX clients. It is possible to poison this XML block. Not uncommon is the technique to apply recursive payloads to similar-producing XML nodes multiple times. If the engine’s handling is poor this may result in a denial of services on the server. Many attackers also produce malformed XML documents that can disrupt logic depending on parsing mechanisms in use on the server. There are two types of parsing mechanisms available on the server side – SAX and DOM. This same attack vector is also used with Web services since they consume SOAP messages and SOAP messages are nothing but XML messages. Large-scale adaptation of XMLs at the application layer opens up new opportunities to use this new attack vector.

XML external entity reference is an XML property which can be manipulated by an attacker. This can lead to arbitrary file or TCP connection openings that can be leveraged by an attacker. XML schema poisoning is another XML poisoning attack vector which can change execution flow. This vulnerability can help an attacker to compromise confidential information.

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