Author: Melodie Foster
Date: 9th December 2020
As part of Microsoft’s last Patch Tuesday of this year, Microsoft released patches for 58 vulnerabilities earlier this week. Of these vulnerabilities, nine are critical and 46 are rated as important.
While none of these flaws have been reported as being exploited in the wild, they will still need patching, for example, the vulnerability that carries the highest CVSS score, 8.5 would allow for remote code execution in the Hyper-V virtualisation software. There are also three other remote code execution flaws that have been fixed.
In an advisory about the highest rated vulnerability, Microsoft said, “to exploit this vulnerability, an attacker could run a specially crafted application on a Hyper-V guest that could cause the Hyper-V host operating system to execute arbitrary code when it fails to properly validate vSMB packet data.”
Also released this week is guidance to address a vulnerability in the DNS resolver, where Windows recommends changing the maximum UDP packet size to 1221 bytes (equal to 4C5 Hexadecimal), “for responses larger than 4C5 or 1221, the DNS resolver would now switch to TCP.”
The attack relies on sending spoofed UDP messages which will defeat source port being randomised for DNS requests, so by sending a larger number of requests, the DNS queries will switch to TCP and mitigate the flaw.
It is therefore recommended to apply the latest patches. 
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