Security

The good news: no 0-days. The bad news: busy week ahead for Microsoft admins

Microsoft released fixes for 137 CVEs on Tuesday, none of which are known to have been targeted by attackers. But the news is not all good as Redmond rated a whopping 30 flaws as critical, with 14 earning a 9.0 or higher CVSS severity rating, including one perfect 10. 

Plus, everyone who celebrates the monthly patchapalooza event received validation for what we all widely suspected last month: Yes, Redmond (and everyone else, for that matter) is using AI to find a ton more bugs than ever before. And that means a lot more work for all the folks applying and testing the patches. 

“This month's release sits on the larger side of a hotpatch month, and we expect releases to continue trending larger for some time,” Tom Gallagher, VP of engineering at Microsoft Security Response Center, said in a note on this month's Patch Tuesday.

Microsoft also said its secret-until-now AI bug hunting system, codenamed MDASH, found 16 of the vulnerabilities addressed in this month’s release. Redmond additionally announced it is making the tool available to a limited number of customers in private preview, along the lines of Anthropic’s Mythos and Project Glasswing.

In other words: no break for Microsoft admins this May Patch Tuesday.

Let’s take a look at some of the nastiest/most-interesting bugs that also received some of the highest-CVSS ratings this month, coming in hot at 9.8 and 9.9.

First up: CVE-2026-41096. This one is a critical, 9.8-rated Windows DNS Client remote code execution (RCE), and while Redmond says exploitation is “unlikely,” we’d suggest patching it ASAP. It’s due to a heap-based buffer overflow, and no authentication or user interaction is needed to exploit it (it's done by sending a specially crafted DNS response to a vulnerable system), potentially leading to memory corruption and RCE.

“Since the DNS Client runs on virtually every Windows machine, the attack surface is enormous,” Zero Day Initiative bug hunting boss Dustin Childs warned. “An attacker with a position to influence DNS responses (MitM, rogue server) could achieve unauthenticated RCE across your enterprise.”

Plus, it could happen across a ton of enterprise systems very rapidly, Jack Bicer, Action1 vulnerability research director told The Register. “This CVE requires immediate attention,” he said. “Successful attacks may lead to widespread endpoint compromise, ransomware deployment, credential harvesting, and operational disruption across corporate networks.”

Another especially bad bug, CVE-2026-42898 in Microsoft Dynamics 365 on-premises systems, achieved a near-perfect 9.9 CVSS rating and also leads to RCE. Any authenticated user can trigger this vuln - it doesn’t require admin or other elevated privileges. 

As Redmond explains: “An attacker with the required permissions could modify the saved state of a process session in Dynamics CRM and trigger the system to process that data, which could result in the server unintentionally executing malicious code.”

Since exploitation could lead to a scope change, meaning the bug can affect systems beyond the vulnerable component, it’s a pretty serious risk to enterprises and should be prioritized. “Scope changes are pretty rare, so if you’re running Dynamics 365 On-Prem, definitely test and deploy this patch quickly,” Childs said.

The second of two 9.8-rated bugs is CVE-2026-41089. It’s a stack-based buffer overflow in Windows Netlogon that allows an unauthenticated, remote attacker to execute code on vulnerable machines by sending a specially crafted network request to a Windows server acting as a domain controller. As Childs points out: the fact attackers can exploit this flaw without credentials or user interactions makes it wormable “This is the highest-impact bug that requires immediate patching: a compromised domain controller is a compromised domain,” he added.

The silver lining this month for defenders is that the single CVE earning a perfect 10.0 CVSS rating is in Azure DevOps, and doesn’t require users to fix anything.

CVE-2026-42826 is an information disclosure vulnerability in the DevOps toolchain “has already been fully mitigated by Microsoft,” according to Redmond. “There is no action for users of this service to take. The purpose of this CVE is to provide further transparency.” ®