June 19, 2019
Ryan Whitwam

Mozilla Issues Emergency Zero-Day Firefox Patch

Mozilla switched to a Chrome-like release schedule years back and has kept up a consistent release cycle ever since. It doesn’t usually deviate unless there’s a serious issue. Well, there’s a serious issue. Mozilla advises all Firefox users to update to the latest version of the browser as soon as possible. The company has just become aware of a zero-day exploit affecting Firefox, meaning there are nefarious internet forces actively using it.

The latest build and the only one that will protect you from the bug is v67.0.3. You can see which version you’re running by opening the menu, clicking Help, and selecting “About Firefox.” The browser should prompt users to update, but you can do so manually if your browser is not on the latest build — just type “update” in the search bar.

According to Mozilla, the issue is a type confusion vulnerability related to JavaScript. A malicious website can use this to cause an “exploitable crash.” This could let the attacker execute remote code on the system, but they’d still be limited to the browser’s sandbox. That might be enough to do some damage, though.

Mozilla has specifically avoided providing extensive details of the flaw. It only says it knows there are active attacks in the wild, so it probably wants to get users updated first. Otherwise, it could make things even worse.

This screen will tell you what version of the browser you’ve got. Anything lower than 67.0.3 and you’re in trouble. Update immediately.

The original bug report comes from Samuel Groß, who works on Google’s elite Project Zero team, as well as the Coinbase security team. We don’t know much about the nature of the attacks, but Groß’s involvement suggests they may be attempting to exploit the vulnerability to steal cryptocurrency. A UXSS (universal cross-site scripting) coupled with the new JavaScript attack could get them what they need without touching the underlying operating system.

Firefox has managed to avoid frequent emergency updates. The last one was in 2016 when it patched a zero-day exploit that could de-anonymize users of the Tor network.

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