Microsoft's Patch Tuesday: Zero-Day Flaws and Legacy Drivers Terminated
Microsoft takes aim at security vulnerabilities, but the battle never ends. In its first Patch Tuesday of 2026, Microsoft addressed a whopping 114 security issues, one of which was already being actively exploited by attackers.
Among the vulnerabilities, one was labeled as exploited in real-world attacks, and Microsoft acknowledged public disclosure for two others. Interestingly, no critical remote code execution or elevation of privilege vulnerabilities were listed in this batch.
The Exploited Zero-Day:
Adam Barnett, a Lead Software Engineer at Rapid7, shed light on the exploited vulnerability, which resides in the Windows Desktop Window Manager (DWM). The DWM is a prime target for threat actors due to its role in managing the display of content on Windows systems.
"The DWM's responsibility for rendering all visual elements on a Windows display makes it a lucrative target. It provides both privileged access and universal availability, as any process may need to display content," explained Barnett. Despite Microsoft's medium severity rating (CVSS v3 score of 5.5), Barnett emphasized the potential impact of information disclosure vulnerabilities, which often receive lower scores due to their indirect nature.
But here's where it gets controversial: Barnett pointed out that Microsoft rarely marks information disclosure flaws as exploited in the wild, implying that these vulnerabilities might be part of a larger attack chain.
Legacy Drivers and Security Concerns:
Barnett also drew attention to the removal of legacy modem drivers from Windows. In October 2025, Microsoft took action against a specific driver, ltmdm64.sys, due to its involvement in an exploited elevation of privilege vulnerability (CVE-2025-24052).
In the recent updates, two more modem drivers were removed due to similar concerns. Barnett mentioned that Microsoft is aware of functional exploit code for CVE-2023-31096, a vulnerability that was initially published over two years ago via MITRE.
The latest patches eliminate agrsm64.sys and agrsm.sys, drivers that originated from the same third-party developer and have been part of Windows for decades. Barnett assured that most users won't notice the removals, but these drivers may still be present in certain environments, including industrial control systems.
This raises a crucial question: How many more legacy drivers are lurking in fully patched Windows systems, and how long will they continue to be a target for attackers? Barnett emphasized that even without physical modem hardware, systems can remain vulnerable.
Secure Boot Vulnerability:
The Patch Tuesday updates also addressed a critical security feature bypass issue in Windows Secure Boot, identified as CVE-2026-21265. This vulnerability is linked to the transition from older Microsoft root certificates used in the Secure Boot ecosystem.
Microsoft released replacement certificates in 2023, following a bootkit campaign (CVE-2023-24932). Barnett warned that devices still using the 2011 certificates, which will expire later this year, will no longer receive Secure Boot security updates.
Organizations must exercise caution when updating bootloaders and BIOS firmware to avoid rendering systems unbootable due to incorrect remediation steps.
Product Support Updates:
Microsoft also announced the end of support for Visual Studio 2022 LTSC 17.10 and Dynamics CRM 2016 (Dynamics 365), encouraging users to upgrade to newer versions. These product lifecycle changes highlight the ongoing commitment to security and stability.
And this is the part most people miss: While Microsoft's efforts to patch vulnerabilities and remove outdated drivers are commendable, the constant emergence of new threats and the persistence of legacy components underscore the never-ending battle against cyberattacks. What do you think? Are we winning the war against zero-day exploits and legacy vulnerabilities, or is it an uphill battle that requires a paradigm shift in cybersecurity strategies?
