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Mozilla eases fears over phishy URL alert

User confusion unlikely

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Mozilla developers have eased concerns about the severity of a security feature in Firefox that often fails to warn users when they've encountered obfuscated URLs that might lead to malicious websites.

Developers of the open-source browser have known of the URL warning bypass since at least June, when it was reported here. Under most circumstances, Firefox will display a warning when users click on links that contain addresses that have been obfuscated to hide their true destination. But when users encounter encoded URLs in inline frames embedded in a webpage, no such alert is delivered.

“This impacts the user security because obfuscated links in the iframes might trick the user to visit false links,” the person reporting the behavior wrote.

On Tuesday, the same person, who turns out to be a researcher from web security firm Armorize, repeated the warning. “In certain cases, it can be used effectively in spreading malware and stealing sensitive information,” Aditya K Sood wrote on the Armorize blog.

But Mozilla said Tuesday that they don't believe the behavior represents much of a risk because the obfuscated links aren't visible during normal surfing, anyway.

“Most users don't look at the HTML source of the pages they are loading, which is the only way you'd encounter this URL,” Johnathan Nightingale, Mozilla's director of Firefox development, said in a statement. “We do not anticipate this bug would cause user confusion or deception.”

The statement went on to remind world+dog that Firefox ships with protection that automatically warns users when they're about to access pages identified in phishing or malware scams.

In his post, Sood also pointed to this link in suggesting that Google Chrome exhibited its own obfuscated URL bypass behavior. ®

The headline and first sentence of this article were updated clarify Mozilla's statement.

Internet Security Threat Report 2014

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