Microsoft’s May 2021 Security Updates Fix Multiple Products’ High-Risk Vulnerabilities

Overview

On May 12, 2021, Microsoft released May 2021 Security Updates to fix 55 vulnerabilities, including high-risk remote code execution and privilege escalation, in widely used products like Microsoft Windows, Office, Exchange Server, Visual Studio Code, and Internet Explorer.

In the vulnerabilities fixed by this month’s security updates, there are four critical vulnerabilities and 50 important ones. Affected users are advised to patch their installations as soon as possible. For the list of vulnerabilities, see the appendix.

NSFOCUS Remote Security Assessment System (RSAS) can detect most of the vulnerabilities (including high-risk ones such as CVE-2021-26419, CVE-2021-31166, CVE-2021-31194, and CVE-2021-28476) fixed by these security updates. Customers are advised to immediately update the plug-in package of their RSAS to V6.0R02F01.2301, which is available at http://update.nsfocus.com/update/listRsasDetail/v/vulsys.

Reference link: https://msrc.microsoft.com/update-guide/en-us/releaseNote/2021-May

Description of Critical Vulnerabilities

Based on the product popularity and vulnerability criticality, we have selected the vulnerabilities with a big impact that users should keep their eyes open for:

HTTP Protocol Stack Remote Code Execution Vulnerability (CVE-2021-31166)

The HTTP protocol stack (http.sys) is prone to a remote code execution vulnerability that allows unauthenticated, remote attackers to execute arbitrary code on the target system by sending crafted packets to a target host. This vulnerability has a CVSS score of 9.8, and is wormable, as Microsoft acknowledges.

For vulnerability details, visit the following link:

https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-31166

Hyper-V Remote Code Execution Vulnerability (CVE-2021-28476)

Windows Hyper-V, a native hypervisor, is prone to a remote code execution vulnerability with a CVSS score of 9.9. This vulnerability allows guest virtual machines (VMs) to force the Hyper-V host kernel to read arbitrary addresses that may be invalid. In certain cases, an attacker who has successfully exploited this vulnerability could execute binaries on the Hyper-V server or execute arbitrary code on the system.

For vulnerability details, visit the following link:

https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-28476

Microsoft SharePoint Remote Code Execution Vulnerabilities (CVE-2021-28474, CVE-2021-31181)

An authenticated attacker could exploit this vulnerability to execute arbitrary code on affected installations of Microsoft SharePoint.

For vulnerability details, visit the following link:

• https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-28474
• https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-31181

OLE Automation Remote Code Execution Vulnerability (CVE-2021-31194)

This vulnerability exists in Windows OLE and could be exploited via a web browser that invokes OLE automation. An attacker could set up a malicious website and trick users into visiting this website, thus achieving remote code execution.

For vulnerability details, visit the following link:

https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-31194

Exchange Server Security Feature Bypass Vulnerability (CVE-2021-31207)

This is one of the vulnerabilities discovered as part of this year’s Pwn2Own competition and its details have been published. An attacker who has successfully exploited this vulnerability could gain a certain degree of control over the server.

For vulnerability details, visit the following link: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-31207

 Scope of Impact

The following table lists affected products and versions that require special attention. Please view Microsoft’s security updates for other products affected by these vulnerabilities.

Mitigation

Patch Update

Currently, Microsoft has released security updates to fix the preceding vulnerabilities in product versions supported by Microsoft. Affected users are strongly advised to apply these updates as soon as possible. These updates are available at the following link:

https://msrc.microsoft.com/update-guide/en-us/releaseNote/2021-May

Note: Windows Update may fail due to network and computer environment issues. Therefore, users are advised to check whether the patches are successfully applied immediately upon installation.

Right-click the Start button and choose Settings (N) > Update & Security > Windows Update to view the message on the page. Alternatively, you can view historical updates by clicking View update history. If an update fails to be successfully installed, you can click the update name to open the Microsoft’s official update download page. Users are advised to click the links on the page to visit the “Microsoft Update Catalog” website to download and install independent packages.

Appendix: Vulnerability List

Statement

This advisory is only used to describe a potential risk. NSFOCUS does not provide any commitment or promise on this advisory. NSFOCUS and the author will not bear any liability for any direct and/or indirect consequences and losses caused by transmitting and/or using this advisory. NSFOCUS reserves all the rights to modify and interpret this advisory. Please include this statement paragraph when reproducing or transferring this advisory. Do not modify this advisory, add/delete any information to/from it, or use this advisory for commercial purposes without permission from NSFOCUS.