Microsoft has officially shipped Hotpatch KB5079420 for Windows 11 versions 24H2 and 25H2 as part of its March 2026 Patch Tuesday security cycle.
While the update is lightweight by design, the surrounding security context makes it one of the more consequential monthly releases of early 2026.
The hotpatch targets OS Builds 26200.7979 and 26100.7979 and delivers what Microsoft describes as “miscellaneous security improvements to internal OS functionality,” a broad but deliberate phrasing that covers kernel-level and subsystem hardening applied without requiring a device reboot.
Microsoft KB5079420 Hotpatch
Unlike traditional cumulative updates, hotpatch releases allow Microsoft to deliver security fixes by patching in-memory code at runtime, meaning eligible Windows 11 Enterprise endpoints can receive security hardening without interrupting active sessions or forcing restart cycles.
This model dramatically reduces mean time to remediation (MTTR) for critical vulnerabilities and has become a central pillar of Microsoft’s Windows servicing strategy for high-uptime environments.
For enterprise administrators managing hundreds or thousands of endpoints, the ability to patch production machines during business hours without scheduling downtime represents a significant operational advantage.
Microsoft confirmed that Windows Autopatch will begin enabling hotpatch updates by default starting with the May 2026 security update, signaling that this delivery mechanism is transitioning from opt-in to standard practice for managed Windows fleets.
Organizations that have not yet evaluated hotpatch eligibility requirements, specifically Windows 11 Enterprise 24H2 or 25H2, enrolled in Autopatch or Azure Arc, should treat April 2026 as a planning deadline.
What Does Microsoft KB5079420 Fix
The KB article for this hotpatch is intentionally sparse on specifics, citing “miscellaneous security improvements to internal OS functionality” across both x64 and ARM64 architectures.
This deliberate vagueness is common in hotpatch updates, where Microsoft avoids publishing granular details that could serve as a roadmap for threat actors attempting to reverse-engineer the patch before broad deployment.
Security teams should note that this is a security-only hotpatch month in Microsoft’s alternating baseline/hotpatch calendar. The March 10 release falls in a hotpatch quarter alongside the broader March 2026 Patch Tuesday cycle, which also shipped KB5079473 (the full cumulative update for 24H2/25H2) and KB5079466 for Windows 11 26H1.
Devices already running the latest baseline build will receive only the delta included in KB5079420, minimizing bandwidth consumption and deployment risk.
Secure Boot Certificate Expiration
The most strategically important disclosure in the KB5079420 release notes is a forward-looking advisory: Secure Boot certificate updates will NOT be delivered with this hotpatch. Instead, Microsoft has confirmed they will arrive with the next baseline Windows update in April 2026.
The widely deployed Microsoft UEFI CA 2011 certificate present on the vast majority of Windows PCs manufactured before 2024 is scheduled to begin expiring in June 2026.
Devices that are not migrated to the newer Windows UEFI CA 2023 certificate before that deadline risk boot failures, broken Secure Boot trust chains, and potential exposure to bootkit-class malware that exploits unsigned or weakly signed boot components.
ASUS and other OEM vendors have already issued independent advisories urging customers to ensure Secure Boot certificates are updated before mid-2026.
Microsoft’s own Secure Boot Playbook, published in November 2025, recommends organizations begin inventorying affected devices immediately, coordinate with OEM firmware update channels, and run pilot validation before deploying certificate changes at scale.
The April 2026 baseline update will be the primary delivery vehicle for this transition, and missing it on even a fraction of enterprise endpoints carries a measurable security risk.
Known Issues and Active Bugs
KB5079420 ships with two actively documented known issues that administrators must track:
1. Microsoft Account Sign-In Failures: Users may experience failures when signing in with a Microsoft account in Microsoft Teams Free and other Microsoft 365 consumer applications after applying this hotpatch.
This issue is connected to a broader account authentication regression introduced in the March 2026 update cycle; Microsoft released an out-of-band emergency fix (KB5085516) to address a similar sign-in failure traced to KB5079473, and organizations should monitor for a comparable resolution targeting hotpatch-affected builds.
2. Reset This PC Feature Failure: A confirmed bug causes the “Reset this PC” (Push Button Reset) function to fail on Windows 11 24H2 and 25H2 systems after installing either the February 2026 hotpatch (KB5077212) or this March hotpatch (KB5079420).
Microsoft has documented this issue and published a specific mitigation: administrators should deploy the March Safe OS Dynamic Update KB5079471, which patches the Windows Recovery Environment (WinRE) layer where the reset process fails. Because this fix targets WinRE rather than the live OS, it needs to be applied only once per affected endpoint.
Installation and Deployment Guidance
KB5079420 is available via Windows Update, Microsoft Update Catalog, and Windows Server Update Services (WSUS). For environments using Windows Update, the latest servicing stack update (SSU KB5083532, version 26100.8035) is bundled and installs automatically alongside the hotpatch.
Devices with earlier updates already installed will pull only the new delta, reducing deployment size and risk.
IT security teams should prioritize deploying KB5079420 before the April 2026 baseline drops, stage KB5079471 alongside it to remediate the Reset this PC bug, and prepare device inventories now for the upcoming Secure Boot certificate rollout. The window between March and June 2026 is not a grace period; it is an active remediation timeline.
FAQ
Q1: Does KB5079420 require a device restart?
No, the hotpatch update, KB5079420, applies security fixes to in-memory code without requiring a reboot on eligible Windows 11 Enterprise 24H2/25H2 systems.
Q2: Will the Secure Boot certificate update come with KB5079420?
No, Microsoft confirmed Secure Boot certificate updates are deferred to the April 2026 baseline Windows update, not this March hotpatch.
Q3: What is the fix for the Reset This PC failure after KB5079420?
Install the March Safe OS Dynamic Update KB5079471, which patches WinRE and resolves the Push Button Reset failure introduced by this hotpatch.
Q4: Which Windows 11 versions are eligible to receive hotpatch updates?
Windows 11 Enterprise editions running version 24H2 or 25H2, enrolled in Windows Autopatch or managed via Azure Arc, are eligible for hotpatch delivery.
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