This week was the first Microsoft Patch Tuesday of 2023, where a total of 98 different vulnerabilities have been patched, including an actively exploited zero-day flaw. This update addresses twice the number of vulnerabilities as the December 2022 Patch Tuesday, which saw fixes for 49 vulnerabilities and 2 zero-day flaws.  

Eleven of the vulnerabilities patched this month have been given a critical severity rating due to the possible resulting impact of an exploit. These critical flaws include 5 Windows Layer 2 Tunnelling Protocol and 2 Windows Secure Socket Tunnelling Protocol (SSTP) vulnerabilities that could result in remote code execution, 3 Privilege escalation vulnerabilities for Windows Cryptographic Services vulnerabilities, and a Microsoft Office SharePoint Server vulnerability, CVE-2023-21743, that can result in a security feature bypass. 

The high severity Zero-day flaw CVE-2023-21674 is an elevation of privilege vulnerability found in the Windows Advanced Local Procedure Call (ALPC).  Windows ALPC is an inter-process communication mechanism used for passing high speed messages between Windows operating system components. An exploit can take place without any user interaction, where an authorised attacker with basic user privileges can perform a browser sandbox escape, resulting in disrupted availability of the component. If this vulnerability was successfully exploited the attacker could go on to gain SYSTEM level privileges on the device.  

Microsoft warned users that this vulnerability has a public disclosed exploit via their default vulnerabilities notification service, however the exploitability assessment provided on the Microsoft Security Response Center update guide states this vulnerability is not publicly disclosed, but exploitation has been detected in the wild. Users should apply the recent Patch Tuesday updates as soon as possible in order to be best protected against attacks. The Microsoft Security Update Guide contains download links for Monthly Rollup and Security Rollup updates for all actively supported Windows and Microsoft products, and includes details of the CVEs fixed in each update.