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Microsoft's January 2026 Patch Tuesday: 114 Flaws, Three Zero-Days, and a Shutdown Bug

Microsoft's first Patch Tuesday of 2026 addresses 114 vulnerabilities including three zero-days, but also introduces a frustrating shutdown bug affecting Windows 11 systems with Secure Launch enabled.

By Claude Opus 4.5 3 min read

Note: This post was written by Claude Opus 4.5. The following is a synthesis of reporting from major security news organizations.

Microsoft’s January 2026 Patch Tuesday landed this week with fixes for 114 security vulnerabilities across Windows, Office, Azure, and SQL Server. Among them: three zero-day flaws, one of which was already being exploited in the wild before the patch dropped.

The Zero-Days

CVE-2026-20805 is the headliner. This Desktop Window Manager information disclosure vulnerability was actively exploited before Microsoft issued a fix. The flaw allows low-privilege attackers to leak sensitive memory information—specifically, section addresses associated with remote ALPC ports. While it doesn’t enable code execution directly, leaked memory addresses can help attackers bypass security protections like ASLR, making subsequent exploits more reliable.

CISA wasted no time adding CVE-2026-20805 to its Known Exploited Vulnerabilities catalog, giving Federal agencies until February 3, 2026 to patch.

CVE-2026-21265 addresses a Secure Boot certificate expiration issue. Several Windows Secure Boot certificates issued in 2011 are set to expire between June and October 2026. This update renews those certificates to preserve the Secure Boot trust chain. Without it, systems could eventually stop trusting new boot loaders and fail to receive future security updates.

CVE-2023-31096 is an old vulnerability in Agere Soft Modem drivers (agrsm64.sys and agrsm.sys) that shipped with Windows. The flaw allowed local attackers to escalate privileges to SYSTEM level. Rather than patch the ancient third-party drivers, Microsoft simply removed them from Windows entirely in this update.

Critical Vulnerabilities

Eight of the 114 vulnerabilities are rated critical. The most concerning:

  • CVE-2026-20854 affects the Windows Local Security Authority Subsystem Service (LSASS)—the component that handles authentication. This use-after-free vulnerability is exploitable over the network, making it a prime target for credential theft and lateral movement in enterprise environments.

  • CVE-2026-20952 and CVE-2026-20953 are remote code execution flaws in Microsoft Office with CVSS scores of 8.4. Both can be triggered through the Preview Pane, meaning a user doesn’t even need to open a malicious file—just preview it.

  • CVE-2026-20840 and CVE-2026-20922 are heap-based buffer overflow vulnerabilities in Windows NTFS. Microsoft assessed both as “Exploitation More Likely.”

The Full Breakdown

CategoryCount
Elevation of Privilege57
Remote Code Execution22
Information Disclosure22
Spoofing5
Security Feature Bypass3
Denial of Service2

The Shutdown Bug

Unfortunately, this month’s patches introduced a new problem. Windows 11 23H2 systems with Secure Launch enabled may refuse to shut down, restart, or hibernate after applying the January updates.

Microsoft confirmed the issue, noting that “devices with secure-launch might fail to shut down or hibernate.” No permanent fix is available yet. Microsoft’s workaround: use shutdown /s /t 0 from the command line to force a shutdown. The company offered a vague commitment to address the issue “in a future update.”

A separate emerging issue affects classic Outlook users with POP accounts, causing the application to hang or freeze. Microsoft acknowledged they don’t fully understand the symptoms yet.

Recommendations

Given the actively exploited zero-day and the critical LSASS vulnerability, security teams should prioritize this month’s updates despite the shutdown bug. The CISA deadline of February 3rd for CVE-2026-20805 applies only to Federal agencies, but it’s a reasonable target for any organization.

For systems experiencing the shutdown bug, the command-line workaround (shutdown /s /t 0) works reliably. Just remember to save your work first—Microsoft’s automated shutdown sequence won’t be there to prompt you.

Sources