Critical Patches Issued for Microsoft Products, April 13, 2021

DESCRIPTION:
Multiple vulnerabilities have been discovered in Microsoft products, the
most severe of which could allow for arbitrary code execution in the
context of the logged on user. Depending on the privileges associated
with the user, an attacker could then install programs; view, change, or
delete data; or create new accounts with full user rights. Users whose
accounts are configured to have fewer user rights on the system could be
less impacted than those who operate with administrative user rights.

IMPACT:
Multiple vulnerabilities have been discovered in Microsoft products, the
most severe of which could allow for arbitrary code execution.

A full list of all vulnerabilities can be found at the link below:
https://msrc.microsoft.com/update-guide/en-us

Successful exploitation of the most severe of these vulnerabilities
could result in an attacker gaining the same privileges as the logged-on
user. Depending on the privileges associated with the user, an attacker
could then install programs; view, change, or delete data; or create new
accounts with full user rights. Users whose accounts are configured to
have fewer user rights on the system could be less impacted than those
who operate with administrative user rights.

The following CVEs were disclosed publicly but are not known to be
exploited in the wild:

* CVE-2021-27091 – RPC Endpoint Mapper Service Elevation of Privilege
Vulnerability
* CVE-2021-28312 – Windows NTFS Denial of Service Vulnerability
* CVE-2021-28437 – Windows Installer Information Disclosure
Vulnerability – PolarBear
* CVE-2021-28458 – Azure ms-rest-nodeauth Library Elevation of Privilege
Vulnerability

CVE-2021-28310 (Win32k Elevation of Privilege Vulnerability) was
discovered by Kaspersky and they are reporting that this vulnerability
is possibly being exploited by the BITTER APT group.

SYSTEM AFFECTED:
* Azure AD Web Sign-in
* Azure DevOps
* Azure Sphere
* Microsoft Edge (Chromium-based)
* Microsoft Exchange Server
* Microsoft Graphics Component
* Microsoft Internet Messaging API
* Microsoft NTFS
* Microsoft Office Excel
* Microsoft Office Outlook
* Microsoft Office SharePoint
* Microsoft Office Word
* Microsoft Windows Codecs Library
* Microsoft Windows Speech
* Open Source Software
* Role: DNS Server
* Role: Hyper-V
* Visual Studio
* Visual Studio Code
* Visual Studio Code – GitHub Pull Requests and Issues Extension
* Visual Studio Code – Kubernetes Tools
* Visual Studio Code – Maven for Java Extension
* Windows Application Compatibility Cache
* Windows AppX Deployment Extensions
* Windows Console Driver
* Windows Diagnostic Hub
* Windows Early Launch Antimalware Driver
* Windows ELAM
* Windows Event Tracing
* Windows Installer
* Windows Kernel
* Windows Media Player
* Windows Network File System
* Windows Overlay Filter
* Windows Portmapping
* Windows Registry
* Windows Remote Procedure Call Runtime
* Windows Resource Manager
* Windows Secure Kernel Mode
* Windows Services and Controller App
* Windows SMB Server
* Windows TCP/IP
* Windows Win32K
* Windows WLAN Auto Config Service

RECOMMENDATIONS:
We recommend the following actions be taken:

* Apply appropriate patches or appropriate mitigations provided by
Microsoft to vulnerable systems immediately after appropriate testing.
* Run all software as a non-privileged user (one without administrative
rights) to diminish the effects of a successful attack.
* Remind all users not to visit untrusted websites or follow links
provided by unknown or untrusted sources.
* Inform and educate users regarding threats posed by hypertext links
contained in emails or attachments especially from untrusted sources.
* Apply the Principle of Least Privilege to all systems and services.

REFERENCES:
https://msrc.microsoft.com/update-guide
https://msrc.microsoft.com/update-guide/releaseNote/2021-Apr
https://www.bleepingcomputer.com/news/microsoft/microsoft-april-2021-patch-tuesday-fixes-108-flaws-5-zero-days/