Microsoft’s January 2026 Patch Tuesday update, identified as KB5074109, has made significant strides in bolstering the security of its product ecosystem by addressing a total of 114 vulnerabilities. Among these, a critical zero-day vulnerability affecting the Windows Desktop Window Manager (DWM) has been particularly noteworthy, as it has been actively exploited in the wild.
Key Vulnerabilities Addressed
The update is applicable to Windows 11 versions 24H2 and 25H2 and encompasses essential fixes, security enhancements, and updates to AI components. A standout issue resolved this month is CVE-2026-20805, which pertains to a locally exploitable information disclosure vulnerability within the Desktop Window Manager. This flaw enables attackers with local access and minimal privileges to extract sensitive memory data by exploiting DWM’s interaction with Advanced Local Procedure Call (ALPC) ports. This vulnerability was identified and reported by Microsoft’s Threat Intelligence Center and Security Response Center, although specific technical details remain sparse.
In addition to the zero-day vulnerability, Microsoft has also addressed several high-severity vulnerabilities categorized as “exploitation more likely,” indicating an increased risk of potential attacks. These vulnerabilities include:
- CVE-2026-20816 – A privilege escalation vulnerability in Windows Installer
- CVE-2026-20817 – A flaw in Windows Error Reporting that could allow elevation of privilege
- CVE-2026-20840 – A vulnerability in Windows NTFS
- CVE-2026-20843 – A flaw in the Routing and Remote Access Service (RRAS) component
- CVE-2026-20860 – A vulnerability in the Ancillary Function Driver for WinSock
- CVE-2026-20871 – Another DWM vulnerability distinct from the exploited zero-day
These vulnerabilities, deeply embedded in core Windows 11 functionalities, represent appealing targets for attackers seeking to escalate privileges or navigate laterally within enterprise environments.
Moreover, the KB5074109 update also signals a shift in support, as it removes legacy modem drivers, including agrsm64.sys and smserial.sys, effectively phasing out hardware reliant on these components. This decision appears to stem from a desire to minimize the attack surface by retiring outdated and infrequently used components.
Additionally, the update addresses reliability concerns within Azure Virtual Desktop, specifically resolving RemoteApp connection failures that have surfaced following previous updates. Microsoft has also rectified a WSL networking issue that disrupted corporate VPN access under mirrored networking configurations introduced in earlier builds.
Power efficiency has not been overlooked; devices equipped with Neural Processing Units (NPUs) will now correctly enter idle states, addressing a previous issue where NPUs remained powered while idle, resulting in unnecessary battery drain.
For organizations utilizing Windows Deployment Services (WDS), hands-free deployment is now disabled by default. Administrators are required to explicitly re-enable this functionality, adhering to hardening guidelines aimed at reducing attack vectors during operating system imaging and rollout.
Windows 11 users can easily install the latest security update by navigating to Settings > Windows Update > Check for updates > Install all. The updates will be automatically downloaded and installed, necessitating a system reboot for full application. Users are advised to back up important data prior to initiating the process to mitigate any risk of data loss.
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