Microsoft Office: code execution flaw under attack

What is affected

Microsoft Office is found on ordinary personal computers and phones, so this is not only a problem for companies. If you use it and have not updated since the fix was released, you are exposed.

Microsoft Office Object Linking & Embedding (OLE) dynamic link library (DLL) contains a side loading vulnerability due to it improperly validating input before loading libraries. Successful exploitation allows for remote code execution.

What an attacker can do

This is a code execution flaw. It lets an attacker run their own commands or programs on the affected system. In practice that usually means taking it over: installing malware, stealing data or using it to reach other devices on the same network.

How it is reached

Needs access to the device or a file opened on it

Access the attacker needs

No account needed

Does the victim have to do something?

Yes, the victim must open or click something

What to do

1. Update Microsoft Office now. Open the update or "About" screen, install whatever is offered and restart the app or device, because the fix is not active until you do.
2. Turn on automatic updates so the next fix arrives without you having to look for it.
3. If your device is too old to receive this update, stop using the affected app for anything sensitive and plan a replacement.

Apply updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on November 3, 2021, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 3, 2022, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 43% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99% of all scored vulnerabilities.

Its CVSS severity score is 7.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Microsoft Visio 2007 SP3, Visio 2010 SP2, Visio 2013 SP1, Visio 2016, Visio Viewer 2007 SP3, and Visio Viewer 2010 mishandle library loading, which allows local users to gain privileges via a crafted application, aka "Microsoft Office OLE DLL Side Loading Vulnerability."