A number of Windows versions are affected: Windows 10, Windows 8.1, Windows 7, Windows Server 2008, Windows Server 2012, Windows Server 2019, Windows Server, version 1803 (Server Core Installation), Windows Server, version 1903 (Server Core installation), and Windows Server, version 1909 (Server Core installation). A full list of the affected products can be seen here.
The company said in an advisory on Monday that there were vulnerabilities that could be exploited remotely, due to the way that the Windows Adobe Type Manager handled a specially crafted multi-master font in the Adobe Type 1 PostScript format.
An attacker would be able to exploit this flaw in a number of ways, one of them being by convincing a user to open a document that was made for this specific task or viewing it in the Windows Preview pane.
"Updates that address security vulnerabilities in Microsoft software are typically released on Update Tuesday, the second Tuesday of each month," the company said.
"This predictable schedule allows for partner quality assurance and IT planning, which helps maintain the Windows ecosystem as a reliable, secure choice for our customers."
In the interim, Microsoft said it was recommending the disabling of the preview pane and details pane in Windows Explorer as a workaround. Another workaround was to disable the WebClient service and a third was to rename the ATMFD.DLL file.
Details of the workarounds are here. Microsoft did not specify who had discovered the vulnerability.
Asked for his comments on the vulnerability, former NSA hacker Jake Williams told iTWire: "Microsoft moved font processing out of kernel mode in after the RTM version of Windows 10. But prior to that, fonts were processed entirely in the kernel (which is as crazy as it sounds, but offered better performance).
"But because you can embed fonts in documents, this means that a font-processing vulnerability can give an attacker remote code execution.
"Interestingly, if the preview pane is enabled in Explorer, just clicking the document in the file explorer (without opening it) can give execution in some cases as well (I'm pretty sure that's the case here).
"The type of execution is dependent on the version of Windows, but this is pretty clutch for Windows 7 since there likely aren't patches coming for most orgs still using it."