Microsoft says multiple threat actors, including ransomware affiliates, are targeting the recently patched Windows MSHTML remote code execution security flaw.

In the wild exploitation of this vulnerability began on August 18 according to the company, more than two weeks before Microsoft published a security advisory with a partial workaround.

According to telemetry data analyzed by security analysts at the Microsoft 365 Defender Threat Intelligence Team and the Microsoft Threat Intelligence Center, the small number of initial attacks used maliciously crafted Office documents.

“Since the public disclosure, Microsoft has observed multiple threat actors, including ransomware-as-a-service affiliates, adopting publicly disclosed proof-of-concept code into their toolkits,” the researchers added.

Microsoft recommends immediately applying the CVE-2021-40444 security updates released during the September 2021 Patch Tuesday to block incoming attacks.

The security updates released by Microsoft address the vulnerability for all affected Windows versions and include a Monthly Rollup, a Security Only update, and an Internet Explorer cumulative update.