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By | Dan Goodin 19th November 2007 20:28

Thumb twiddling Mozilla promises fix for privacy-biting bug

Your door is a jar

Mozilla's head of security has promised a patch for a dangerous vulnerability that's been lurking in the popular Firefox browser for more than eight months.

The new urgency in fixing the jar: protocol handler comes after bloggers in recent weeks demonstrated how the vulnerability could wreak real-world havoc, including allowing attackers to steal a victim's Gmail contacts. Short for Java Archive, the jar: protocol is used to compress Java classes and other types of files into a single file. Problem is, the protocol will open any zip-formatted file without first validating the MIME type of the archived contents. Malicious content is then run in the context of a trusted site.

"An attacker can use this to evade filtering on sites that allow users to upload content and use this [to] initiate a cross site scripting attack," Window Snyder, Mozilla's security chief, wrote in this post on the Mozilla Security blog. "This may allow the attacker to access information stored on the trusted site without the victim's knowledge."

The vulnerability is present in Firefox running on Linux, OS X and Windows, Snyder said, speaking through a Mozilla spokesman.

Firefox developers are also working to patch a second, related vulnerability that allows attackers to execute malicious code by linking it to trusted sites with open redirects. Both holes will be plugged in version, which is in the process of being tested. Until it is released, Firefox users should use the latest version of NoScript.

The jar: protocol bug is the latest uniform resource identifier (URI) protocol handler flaw to threaten browser users. It was first identified in February by Mozilla's Jesse Ruderman, but efforts to eradicate the bug languished.

Mozilla bug squashers reaffirmed their commitment to fix the security flaw after Petko D. Petkov on Nov. 7 published a blog entry titled "Web Mayhem: Firefox’s JAR: Protocol issues." In it, he warned the flaw could be exploited to cause a wide variety of trusted sites to turn against people using the Firefox browser.

"Potential targets for this attack include applications such as web mail clients, collaboration systems, document sharing systems, almost everything that smells like Web 2.0, etc, etc, etc.," Petkov wrote.

Shortly thereafter, a researcher known as Bedford demonstrated how attackers exploit the flaw to steal a victim's Gmail contacts.

The jar: protocol bug is only the latest security vulnerability to revolve around the URI protocol, which allow browsers to launch email readers and other programs based on commands that are embedded into a web address. Over the past few months, URIs have emerged as one of the weaker links in the online security chain and are known to have plagued users of Firefox, Internet Explorer and Adobe's Reader and Acrobat programs. ®

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