Microsoft has released security patches this month as part of Patch Tuesday release cycle to address 55 vulnerabilities across Windows, Azure, Visual Studio, Windows Hyper-V, and Office, including fixes for two actively exploited zero-day bugs in Excel and Exchange Server that could be abused to take control of an affected system.

Of the 55 glitches, six are rated Critical and 49 are rated as Important in severity, with four others listed as publicly known at the time of release. 

"Earlier this year, Microsoft alerted that APT Group HAFNIUM was exploiting four zero-day vulnerabilities in the Microsoft Exchange server," said Bharat Jogi, director of vulnerability and threat research at Qualys.

"This evolved into exploits of Exchange server vulnerabilities by DearCry Ransomware — including attacks on infectious disease researchers, law firms, universities, defense contractors, policy think tanks and NGOs. Instances such as these further underscore that Microsoft Exchange servers are high-value targets for hackers looking to penetrate critical networks," Jogi added.