Mozilla caught napping on URL protocol handling flaw

Uh-oh. The latest twist in the URL protocol handling vulnerability saga has left eggs on the faces of the security folks at Mozilla.

It turns out that Mozilla's Firefox is just as guilty Microsoft's Internet Explorer when it comes to passing dangerous data to third party applications.

Over the last two weeks, Mozilla has steadfastly pinned the blame on the URL protocol handling bug on Microsoft, insisting there's a critical IE flaw that remains unfixed but, as a Windows internals expert discovered yesterday, Mozilla might want to be careful about throwing stones.

"Firefox is subject to the exact same flaw that they blame on IE," says Jesper Johansson, a former Microsoft security strategist who has been tracking this bug closely.

Johansson has published proof that Firefox also does not escape quotes in URLs before it passes them on to protocol handlers, a dangerous situation that could lead to code execution attacks.

Interestingly, Johansson does not view this as a browser vulnerability, insisting that the onus is on the application receiving the data to properly validate inputs.

Mozilla's security chief Window Snyder has fessed up to the gaffe exposed by Johansson:

Over the weekend, we learned about a new scenario that identifies ways that Firefox could also be used as the entry point. While browsing with Firefox, a specially crafted URL could potentially be used to send bad data to another application.

We thought this was just a problem with IE. It turns out, it is a problem with Firefox as well. We should have caught this scenario when we fixed the related problem in 2.0.0.5. We believe that defense in depth is the best way to protect people, so we’re investigating it now.

More information on Mozilla's investigation at this Bugzilla entry.