Microsoft patches 112 CVEs on first Patch Tuesday of 2026

Microsoft has pushed fixes for 112 common vulnerabilities and exposures (CVEs) on the first Patch Tuesday of 2026, among them a number of zero-day flaws that were either publicly disclosed or actively exploited prior to patching, and no fewer than eight critical bugs.

Although this is a sharp increase in comparison to recent Patch Tuesdays – December 2025 saw Microsoft patch just 56 flaws – it is important to note that the festive season is frequently a quieter time for patches, sometimes by design, and January often brings an uptick in disclosures. Nevertheless, observed Jack Bicer, director of vulnerability research at patch management firm Action1, the volume of fixes in the latest update underscores “growing pressure” on security teams.

“This comes against a broader trend: in 2025, reported vulnerabilities increased by 12% over 2024, continuing the upward trajectory of disclosed security flaws,” said Bicer.

Paramount among these flaws is CVE-2026-20805, an information disclosure vulnerability in Desktop Window Manager, discovered by Microsoft’s own Threat Intelligence and Security Response Centers.

Although it bears a relatively low Common Vulnerability Scoring System (CVSS) score of just 5.5, active exploitation of CVE-2026-20805 has been observed in the wild, Microsoft said

“The flaw leaks a memory address from a remote ALPC [Asynchronous Local Procedure Call] port. This type of information disclosure vulnerability is often used to defeat Address Space Layout Randomisation (ASLR) – a security feature in modern operating systems designed to protect against buffer overflows and other exploits that rely on manipulating the memory of a running application,” explained Immersive senior director of cyber threat research, Kev Breen.

“Once they know where code resides in memory, they can chain this with a separate code execution bug to turn a difficult exploit into a reliable one,” he said. “Microsoft doesn't provide any information on what other components that chain could involve – making it harder for defenders to threat hunt for potential exploitation attempts, meaning patching quickly is the only mitigation for now.”

Ivanti vice president of security product management, Chris Goettl, agreed with this assessment. “The vulnerability affects all currently supported and extended security update supported versions of the Windows OS,” he said, “[so] a risk-based prioritisation methodology warrants treating this vulnerability as a higher severity than the vendor rating or CVSS score assigned.” 

Next up is a security feature bypass (SFB) flaw in Secure Boot Certificate Expiration, tracked as CVE-2026-21265. It, too, carries a comparatively low CVSS score and Microsoft only rates it as Important. However, said Goettl, it has been publicly disclosed and security teams would be wise to look into it.

“The fix provides a warning regarding certificates that will be expiring in 2026 and details on actions that are required to up renew certificates prior to their expiration in addition to the update,” he said.

“It is recommended to start investigating what actions your organisation may need to take to prevent potential serviceability and security as certificates expire.”

The remaining items on the zero-day list – again both publicly disclosed but not known to be exploited, date back three and four years respectively. Both are elevation of privilege (EoP) flaws affecting soft modem drivers that ship natively with supported Windows operating systems.

The older of the two, CVE-2023-31096, is to be found in Agere Soft Modem Driver, and the more recent one, CVE-2024-55414 in Windows Motorola Soft Modem Driver. Microsoft’s solution is to remove the affected drivers, agrsm64.sys and arsm.sys in the first instances and smserl64.sys and smserial.sys in the second, as part of the January cumulative update.

This means soft modem hardware that depends on them will now cease to work on Windows. Microsoft said admins should act quickly to remove any existing dependencies on the affected hardware.