Microsoft warns that hackers are actively exploiting a vulnerability in Office 365 and Office 2019. The vulnerability is in Mshtml, a browser renderer from Internet Explorer, which is also used for Office documents.
According to a Microsoft advisory, the vulnerability affects Windows 8.1 and Windows 10, as well as Windows Server versions from 2008 to 2019. In order to take advantage of the vulnerability, hackers would send victims modified Microsoft Office documents. If users open those documents without enabling security protections, the vulnerability could allow for remote code execution to be performed on their computers. The vulnerability has been assigned the name CVE-2021-40444 and has been assigned a severity rating of 8.8 out of 10.
Unknown documents, on the other hand, are opened in Protected View or Application Guard mode when Microsoft Office is configured in its default setting. The former is a read-only mode, whereas Application Guard isolates unfamiliar documents, preventing them from gaining access to the systems of their respective owners or users. The vulnerability cannot be exploited while operating in these modes. In addition, the Windows Defender antivirus program and Windows Defender for Endpoint (version 1.349.22.0) provide protection against the vulnerability, according to Microsoft. However, the vulnerability has not yet been addressed in the Windows operating system itself.
The vulnerability was discovered after Expmon security experts discovered a "very sophisticated zero-day assault" targeting Microsoft Office users on Twitter, according to the company. They were able to successfully reproduce the assault on the most recent versions of Office 2019 and Office 365 running on Windows 10 operating system.
Microsoft has not yet released a security upgrade for its Windows operating systems. It has not yet been verified whether or not Microsoft will provide a patch for this vulnerability during the next Patch Tuesday, which is slated for September 14. There is a workaround provided by the IT giant. The installation of all ActiveX elements in Internet Explorer can be disabled in the registry by users by editing the IE registry.
Microsoft warns users against active zero-day exploit vulnerabilities in Office 365 and Office 2019.
