Vulristics: Microsoft Patch Tuesdays Q2 2021

Hello everyone! Let's now talk about Microsoft Patch Tuesday vulnerabilities for the second quarter of 2021. April, May and June. Not the most exciting topic, I agree. I am surprised that someone is reading or watching this. For me personally, this is a kind of tradition. Plus this is an opportunity to try Vulristics in action and find possible problems. It is also interesting to see what VM vendors considered critical back then and what actually became critical. I will try to keep this video short.

First of all, let's take a look at the vulnerabilities from the April Patch Tuesday. 108 vulnerabilities, 55 of them are RCEs. Half of these RCEs (27) are weird RPC vulnerabilities. "Researcher who reported these bugs certainly found quite the attack surface". The most critical vulnerability is RCE in Exchange (CVE-2021-28480). This is not ProxyLogon, this is another vulnerability. ProxyLogon was in March. And this vulnerability is simply related to ProxyLogon, so it is believed that it is exploited in the wild as well. In the second place this Win32k Elevation of Privilege (CVE-2021-28310). It is clearly mentioned in several sources as being used in real attacks. "Bugs of this nature are typically combined with other bugs, such as a browser bug or PDF exploit, to take over a system". And the only vulnerability with a public exploit is the Azure DevOps Server Spoofing (CVE-2021-28459). Previously known as Team Foundation Server (​TFS), Azure DevOps Server is a set of collaborative software development tools. It is hosted on-premises. Therefore, this vulnerability can be useful for attackers.

Let's take a look at May. A very small Patch Tuesday. There are only 55 vulnerabilities. Vendors mainly wrote about HTTP Protocol Stack Remote Code Execution Vulnerability. But no catastrophe happened. "tenable: On May 16, security researcher 0vercl0k published PoC code to github for CVE-2021-31166. Based on our analysis, this exploit could only result in a denial of service (DoS) condition". VM vendors also wrote a lot about Hyper-V Remote Code Execution Vulnerability. But there was no real exploitation there either. But a real exploit appeared for Remote Code Execution in Microsoft SharePoint (CVE-2021-31181). And exploitation in the wild was mentioned for Windows Container Manager Service (CVE-2021-31167), which no VM vendor mentioned at all. But the exploitation was "Personally observed in an environment", so this may not be accurate. Also take a look at Memory Corruption in Microsoft Scripting Engine (CVE-2021-26419) with a public exploit and Information Disclosure in Windows Wireless Networking (CVE-2020-24587) with a sign of exploitation in the wild (but this also may not be accurate).

And finally June. There are even fewer vulnerabilities, only 49. But there are a lot of them with a sign of exploitation in the wild. And this information is directly from Microsoft. Windows MSHTML Platform Remote Code Execution (CVE-2021-33742). Elevations of Privilege in Windows NTFS (CVE-2021-31956), Microsoft Enhanced Cryptographic Provider (CVE-2021-31199, CVE-2021-31201), Microsoft DWM Core Library (CVE-2021-33739). Windows Kernel Information Disclosure (CVE-2021-31955). Much more than usual. VM vendors have written the most about EoP in Windows NTFS (CVE-2021-31956). Do you know what vulnerability they didn't highlight at all? Elevations of Privilege and later Remote Code Execution in Windows Print Spooler (CVE-2021-1675). The one that started the PrintNightmare story. Very ironic. Also pay attention to Spoofing in Microsoft SharePoint (CVE-2021-31950) for which there is a public Server-Side Request Forgery exploit. VM vendors also did not write anything about this vulnerability in their reviews.

Full Vulristics reports:

• ms_patch_tuesday_april2021_report_avleonov_comments.html
• ms_patch_tuesday_may2021_report_avleonov_comments.html
• ms_patch_tuesday_june2021_report_avleonov_comments.html