“An attacker could craft a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights,” Microsoft explained.
It was given a severity rating of 8.8 (out of 10), though Microsoft said any potential attacks would not get very far if the user was running default settings in Office. In those instances, untrusted documents on the web would open in Protected View mode or Application Guard, depending on the version of Office.
“This attack is more dangerous than macros because any organization that has chosen to disable or otherwise limit Macro execution will still be open to arbitrary code execution simply as the result of opening an Office document,” vulnerability analyst Will Dormann told the site.
Microsoft also said that its Defender antivirus program would detect the threat and protect users, assuming it was up to date. Nevertheless, Microsoft is now recommending that users install the newly released patch right away.
“Microsoft has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately,” Microsoft states.