FireFox users are being HIGHLY encouraged by Mozilla, the maker of FireFox, to update your browsers immediately to patch an exploit that was recently found.
If you are not running at least Firefox 39.0.3, you are at risk of the exploit that has been found on a Russia news web site running an advertisement that would search for sensitive files on your computer and upload them to a server in Ukraine.
Mozilla Foundation Security Advisory 2015-78 was released late yesterday and affects FireFox and FireFox ESR. It’s been fixed in FireFox 39.0.3 and Firefox ESR 38.1.1. It was discovered by security researcher Cody Crews and the exploit was reported as a way to violate the same origin policy and inject script into a non-privileged part of the built-in PDF Viewer.
It’s not known how long this vulnerability has existed or where else it may have been exploited.
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