Firefox hit by critical zero-day vulnerability

Graham Cluley
Graham Cluley
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Firefox
Mozilla has issued a warning that its popular Firefox browser contains a critical vulnerability that is being actively exploited by cybercriminals to distribute malware.

The vulnerability, which was previously unknown, is said to affect versions 3.5 and 3.6 of Firefox.

Security firm Norman reported that the Nobel Peace Prize website was distributing a Trojan horse via the exploit yesterday, although it’s obviously possible that other websites may also be serving up the vulnerability in an attempt to infect visiting users.

Sophos is issuing protection against the malware as Troj/Belmoo-A.

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Mozilla says it is working on a fix, but in the meantime Firefox users might be wise to turn JavaScript off and use the popular NoScript addon.

NoScript is a great idea – I’d never use Firefox without it, and neither should you.


Graham Cluley is an award-winning keynote speaker who has given presentations around the world about cybersecurity, hackers, and online privacy. A veteran of the computer security industry since the early 1990s, he wrote the first ever version of Dr Solomon's Anti-Virus Toolkit for Windows, makes regular media appearances, and is the co-host of the popular "Smashing Security" podcast. Follow him on Twitter, Mastodon, Threads, Bluesky, or drop him an email.

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