Microsoft has released a security advisory that warns of a new zero-day weakness that is currently being exploited on the internet. Depending on how you interpret their choice of wording – “targeted attacks” – the scale seems to be relatively limited for the moment, but given that the compromised app is Microsoft Word and is not limited to a specific version, the potential attack surface is huge. And it gets better: the delivery mechanism is a hacked RTF file that once opened can lead to the targeted machine being completely compromised. While RTF files aren’t as widely used as the default “.doc” and “.docx” formats, they are used to export and import documents from Word to other word processing platforms like Wordperfect, LibreOffice, OpenOffice and Apple Pages.

What this means for you:

Microsoft has issued a temporary fix which merely disables the ability for Word to open RTF files, but as of the moment there is no ETA on a patch delivered by Windows Update. We recommend applying this Fix-it if you are at all unsure what an RTF file is, or how to tell the difference from other Word and Email formats.

The most vulnerable user to this exploit is actually someone who uses Word to view formatted emails delivered via Outlook. Normally, Outlook is not set to view emails using Word by default, so if you didn’t set Outlook to do this, you only have to worry about Word. If you did, disable this feature and use Outlook’s built-in email viewer to read formatted emails. For Word users, don’t open RTF files, even if they come from a trusted source, and don’t send any RTF files, as your recipients may be exercising the same level of caution. If you have to exchange data using RTF, make sure you communicate thoroughly with your recipients, and choose another platform other than email to exchange files, primarily so there is no chance they could mistake a trojaned RTF for a legitimate file.