Click on a single malicious Flash file, and you risk losing control of your router, according to two researchers. GNUCitizen.org’s Petko D. Petkov and Adrian Pastor judge the issue to be “HIGHLY SEVERE!”

So let’s take a step back to examine the issue itself. Between two articles, Petkov and Pastor spent about 2,300 words writing about it, and if you want to fully understand the matter, we’d recommend reading them all.

But, if the what-it-is-and-how-to-fix-it version will satisfy you, Robert McMillan summarizes, “By tricking a victim into viewing a malicious Flash file, an attacker could use UPnP to change the primary DNS (Domain Name System) server used by the router to find other computers on the Internet. This would give the attacker a virtually undetectable way to redirect the victim to fake Web sites.”

McMillan later continues, “The attack is particularly worrisome because it is cross-platform – any operating system that supports Flash is susceptible – and because it is based on features of UPnP and Flash, not bugs that could be easily fixed by Adobe or the router vendors.”

Here’s the good news, though: as far as anyone knows, it’s just the two researchers who know anything about this method of attack. Also – although may be side effects from doing this – Petkov and Pastor give instructions on how to turn UPnP off, and say that doing so should effectively prevent the attack.

It’s rare that we see security researchers use bold, all-capital letters in combination with exclamation marks. You might consider that while thinking through the issue.