Microsoft Releases Windows Update (Dec 2020) to Fix 58 Security Flaws

Microsoft on Tuesday released fixes for 58 newly discovered
security flaws spanning as many as 11 products and services as part
of its final Patch Tuesday of 2020^[1], effectively bringing
their CVE total to 1,250 for the year.

Of these 58 patches, nine are rated as Critical, 46 are rated as
Important, and three are rated Moderate in severity.

The December security release addresses issues in Microsoft
Windows, Edge browser, ChakraCore, Microsoft Office, Exchange
Server, Azure DevOps, Microsoft Dynamics, Visual Studio, Azure SDK,
and Azure Sphere.

Fortunately, none of these flaws this month have been reported
as publicly known or being actively exploited in the wild.

The fixes for December concern a number of remote code execution
(RCE) flaws in Microsoft Exchange (CVE-2020-17132), SharePoint
(CVE-2020-17118 and CVE-2020-17121), Excel (CVE-2020-17123), and
Hyper-V virtualization software (CVE-2020-17095), as well as a
patch for a security feature bypass in Kerberos (CVE-2020-16996),
and a number of privilege escalation flaws in Windows Backup Engine
and Windows Cloud Files Mini Filter Driver.

CVE-2020-17095 also carries the highest CVSS score of 8.5 among
all vulnerabilities addressed in this month’s release.

“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,” Microsoft noted^[2].

Additionally included as part of this month’s release is an
advisory^[3]
for a DNS cache poisoning^[4]
vulnerability (CVE-2020-25705) discovered by security researchers
from Tsinghua University and the University of California last
month.

Dubbed a Side-channel AttackeD DNS attack (or SAD DNS attack^[5]), the flaw could enable
an attacker to spoof the DNS packet, which can be cached by the DNS
Forwarder or the DNS Resolver, thereby re-enabling DNS cache
poisoning attacks.

To mitigate the risk, Microsoft recommends a Registry workaround
that involves changing the maximum UDP packet size to 1,221 bytes
(4C5 Hexadecimal).

“For responses larger than 4C5 or 1221, the DNS resolver would
now switch to TCP,” the Windows maker stated in its advisory.

Since the attack relies on sending spoofed UDP (User Datagram
Protocol) messages to defeat source port randomization for DNS
requests, implementing the tweak will cause larger DNS queries to
switch to TCP, thus mitigating the flaw.

It’s highly advised that Windows users and system administrators
apply the latest security patches to resolve the threats associated
with these issues.

To install the latest security updates, Windows users can head
to Start > Settings > Update & Security > Windows Update,
or by selecting Check for Windows updates.