"Similar ones are discovered every year, in mostly every product version and they can all be used by attackers to run code and install software, requiring no user interaction beyond normal browsing."
This vulnerability is not the exception, but rather the rule, Tanase said. The vulnerability stems from a bug in the way the browser calculates the length for a JavaScript string concatenation. As an example, he pointed to CVE-2013-0750, a remote code execution vulnerability fixed in Firefox 18 a few days ago.
Tanase pointed out that vulnerabilities in the browser's JavaScript rendering engine are not uncommon. "While I am excited to see Firefox giving extra thought to the security of its users, what worries me is that even the technologies on which PDF.js is based can be vulnerable." Such an implementation might provide more security to the end user because its user base will be smaller compared to that of Adobe Reader and cybercriminals will continue to focus on exploiting the most popular pieces of software, Stefan Tanase, a senior security researcher at antivirus vendor Kaspersky Lab, said via email. Security experts believe that the built-in PDF viewer will provide more security for users, but not necessarily because it won't be prone to vulnerabilities as third-party PDF viewer plug-ins are. The company did not immediately respond to a request for comment. Mozilla did not clarify whether this viewer will be used by default even in cases when a third-party PDF viewing plug-in is installed. "The PDF.js powered viewer in Firefox Beta is the first step to it becoming a fully integrated feature within the release version of Firefox so its benefits can be enjoyed by all Firefox users," the Mozilla software engineers said.
A live demo of the viewer running as a Web application is available on the PDF.js website. Since the viewer uses standard HTML5 APIs (application programming interfaces) it can also run in different browsers and on different platforms, like tablets and mobile phones. "Not only do most PDFs load and render quickly, they run securely and have an interface that feels at home in the browser." "The PDF.js project clearly shows that HTML5 and JavaScript are now powerful enough to create applications that could previously have only been created as native applications," the Mozilla software engineers said. The built-in PDF viewer currently being tested stems from a Mozilla Labs project called PDF.js.
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