Windows credential autofill blocked by Jan 2026 security update (CVE-2026-20804)

Microsoft’s January security rollup for Windows quietly removed a long‑used convenience: the ability for some applications and remote tools to autofill credentials into Windows sign‑in dialogs. The change — delivered in the January 13, 2026 cumulative updates (notably KB5074109 and sibling updates for other servicing branches) — intentionally prevents credential dialogs from accepting input that cannot be reliably attributed to a trusted, local source, closing an input‑injection vector linked to a Windows Hello privilege assignment flaw tracked as CVE‑2026‑20804.

Background​

Windows has long balanced two competing operational demands: making remote support and automation productive, and keeping authentication surfaces tightly controlled. Over the years vendors and IT teams adopted a variety of patterns — remote technicians typing passwords through a screen‑share session, virtual on‑screen keyboards inside a remote desktop, automation scripts that synthesize keystrokes, and accessibility helpers that interact with protected UI — to meet real world needs. Those same patterns, however, also created an attack surface that could be abused if an attacker or a compromised app could inject input into privileged sign‑in dialogs.
On Patch Tuesday of January 13, 2026, Microsoft shipped a set of cumulative updates for Windows 11 and Windows 10 that included a deliberate credential‑UI hardening described in the update notes as “Credentials autofill.” The release notes make clear the behavioral change: credential dialogs no longer respond to virtual keyboard input from remote desktop or screen‑sharing tools, and certain automated authentication workflows that previously relied on synthetic keyboard events may fail. Administrators and helpdesk teams quickly noticed breakage in common workflows and reported sign‑in failures in Azure Virtual Desktop and Windows 365 scenarios, prompting targeted follow‑ups and out‑of‑band fixes for specific regressions.
The vulnerability motivating the hardening is tracked publicly as CVE‑2026‑20804 — an incorrect privilege assignment in Windows Hello described by Microsoft and cataloged by vulnerability databases. The issue allows a local attacker to tamper with Windows Hello internals under improper privilege constraints, prompting Microsoft to tighten how authentication UI accepts input. The CVE entry and third‑party vulnerability trackers list the flaw and the associated patches across multiple Windows builds.

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What changed, technically​

Trusted‑input only: a short, concrete rule​

The practical rule Microsoft applied is simple and security‑first: Windows credential UI accepts input only from sources that can be proven local and trusted. That means interactive keystrokes from a physical keyboard are accepted, as are requests from properly configured accessibility tools that have been granted UIAccess and applications running with elevated (administrator) integrity. Input that originates from typical remote screen‑sharing apps, virtual keyboards running in remote sessions, or processes that simulate keyboard events from a lower integrity level will be ignored by credential dialogs.

Attack vectors the change blocks​

• Injected keystrokes produced by automation frameworks that use SendInput/PostMessage or equivalent methods against protected dialogs.
• Virtual on‑screen keyboards or clipboard redirects inside remote sessions that can be controlled remotely.
• Remote technicians or screen‑share agents that type credentials on a remote user’s behalf without a secure delegation mechanism.

Inputs still allowed (and why)​

• Local physical keyboard: hard to spoof from a remote process and strongly correlated with an interactive user.
• UIAccess accessibility apps: allowed when the app is signed, installed in a secure location, and explicitly granted UIAccess by Windows (a high‑barrier requirement by design).
• Elevated administrator processes: elevation is treated as an additional consent and integrity boundary, so elevated processes retain the ability to interact with protected UI. However, elevation changes the trust boundary and has its own risks.

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Why Microsoft did this — threat model and rationale​

Windows authentication dialogs are a high‑value target. If a malicious process can trick the system into accepting injected keystrokes or otherwise feed secrets into a credential box, an attacker can capture credentials, escalate privileges, or subvert authentication flows. Microsoft’s hardening responds to the specific risk surface associated with Windows Hello privilege assignment weaknesses (the CVE noted above) and to the broader class of untrusted input injection into secure UI surfaces. The patch approach is defensive: reduce the number of reliable ways a non‑local or non‑trusted process can affect credential UI.
Security teams and platform engineers consider this the correct defensive posture: attack surface reduction for authentication UI has a direct, measurable payoff. Industry analysts and coverage from security vendors agree that preventing untrusted input into credential dialogs materially reduces opportunities for credential theft during remote support or automated flows. That said, the move is not just technical — it forces an operational re‑assessment for many organizations.

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Who is affected — operations and compatibility​

This is not a niche change. The hardening affects any workflow or third‑party product that relied on programmatically sending keystrokes into Windows credential dialogs. Commonly impacted groups include:

• Helpdesk and support desks that remotely type user passwords during support calls.
• Remote administration and RMM (Remote Monitoring & Management) tools that use keyboard injection as a shortcut to authenticate.
• Test labs, CI pipelines, or deployment scripts that rely on virtual keyboards or SendInput‑style automation to populate credentials in interactive dialogs.
• Cloud PC and Azure Virtual Desktop provisioning scenarios where virtualized keyboard input is used during sign‑in.

Microsoft’s release notes and known‑issues entries make it explicit that enterprise and managed environments are most likely to surface problems; consumers on Home and Pro are less likely to experience the regressions because their operational models rarely depend on scripted or remote autofill. Enterprises should assume they will see an impact and plan accordingly.

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Short‑term mitigations and Microsoft’s guidance​

Microsoft’s documentation and follow‑up advisories describe a temporary mitigation: run the application performing remote credential submission with elevated (administrator) privileges so the process is treated as trusted by the credential UI. That will restore the previous autofill behavior for that elevated process. However, Microsoft cautions this is a temporary, tightly controlled workaround and not a long‑term fix — elevating remote‑control tools expands the trust boundary and increases exposure if the elevated process is compromised.
Operational guidance IT teams should follow immediately:

• Inventory any automated workflows, remote tools, and RMM agents that submit or simulate credential input.
• Test those workflows in a lab after applying the January updates; identify failures and categorize whether they’re business‑critical.
• If a temporary elevation is required, restrict it to the specific tool, apply least‑privilege controls, log and monitor the elevated use, and document the exception for rapid rollback as soon as vendors release compatible updates.
• Prefer architectural changes — use platform credential APIs, service principals, managed identities, or tokenized delegation instead of interactive autofill.

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Medium‑ and long‑term remediation: stop typing passwords for automation​

The only sustainable solution is to remove the practice of typing passwords into the platform credential UI as a mechanism for automation or delegation. Vendors and IT teams should adopt platform‑approved alternatives:

• Use the Windows Credential UI APIs (for example, CredUIPromptForWindowsCredentials) and integrate with supported credential providers rather than simulating keyboard input.
• Implement non‑interactive delegation: service accounts, managed identities, OAuth/modern authentication flows, token exchange, or secure vault integrations (for example, privileged access solutions or secrets managers) that don’t require typing a user’s password into a GUI.
• For accessibility scenarios that genuinely require elevated UI access, implement the UIAccess model properly: sign binaries, install in secure folders, and request UIAccess in the manifest so Windows can consider the app trusted.

These paths require development effort, product updates from remote‑support vendors, and planning from IT architects — but they close brittle, high‑risk patterns and align automation with identity best practices.

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Vendor responsibilities and the compatibility gap​

Third‑party remote‑control, screen‑sharing, and automation vendors are the most immediate stakeholders in the compatibility story. Many vendors historically relied on keyboard synthesis because it is simple and broadly compatible. That compatibility now breaks on patched systems.
Vendors should:

• Publish compatibility statements and timelines showing when their products will support the platform hardening.
• Replace keyboard synthesis with service‑based agents or native calls into credential APIs.
• Offer secure delegation modes (for example, token forwarding or a temporary one‑time code mechanism) rather than instructing technicians to type credentials on behalf of users.
• Provide clear, secure guidance for customers who might temporarily rely on elevation workarounds — and make the workaround easy to track and remove later.

For administrators, vendor SLAs and published compatibility roadmaps must be part of the remediation plan; vendors that don’t commit to fixing keyboard injection will force customers to re‑architect their support processes or replace the tool.

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Security tradeoffs and risks of the common workarounds​

The temptation after a disruptive hardening is predictable: restore functionality quickly. The common fallback — run the remote support tool elevated — does indeed restore credential autofill, but it also dramatically increases the attack surface. An elevated remote agent process can act with administrator privileges and, if compromised, can be used to install persistence, alter security configuration, or exfiltrate secrets.
Practical mitigations if elevation is used:

• Limit elevation strictly to specific machines or dedicated administrative bastions.
• Use conditional access, strong MFA, and network isolation for technicians and management endpoints.
• Apply application allow‑listing and tight code‑signing requirements for the elevated tools.
• Audit, alert, and require post‑use review and revocation of the elevated state as soon as the maintenance operation completes.

Short‑term convenience must be weighed against long‑term risk. Elevation is a bridge — not a destination.

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Real‑world examples: where admins saw the impact​

Reports from enterprise customers and technical observers after January’s rollup highlighted realistic failure modes: sign‑in prompts failing for Azure Virtual Desktop and Windows 365 sessions, helpdesk workflows that previously had technicians type in passwords now stalling, and automation test labs that needed rework. Microsoft acknowledged connection and authentication failures in some cloud‑and‑virtualization scenarios and published targeted updates to address regressions, underscoring that the company anticipated breaking customer workflows and prepared follow‑ups to reduce operational pain while preserving the security posture.
Independent coverage of January’s patches emphasized the scale of the release (more than 100 fixes in many branches), the active zero‑day the release addressed, and the fact that the credential UI hardening was one of several high‑impact changes enterprises needed to test quickly. Those broader reporting threads provide context that the credential hardening was part of a larger, high‑urgency security baseline for the platform.

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Practical checklist for Windows admins — next 30 days​

• Inventory: Identify every remote‑support tool, RMM agent, automation script, and deployment flow that interacts with credential dialogs.
• Test: Apply January updates to a representative lab and run each workflow; document failures and workarounds required.
• Communicate: Tell helpdesk and support teams that they may no longer be able to type passwords remotely and provide alternative processes (e.g., user‑entered one‑time passcodes or token handoff).
• Mitigate: If absolutely necessary, use scoped elevation for a single process with compensating controls — log, monitor, and remove as soon as possible.
• Modernize: Prioritize replacing keyboard‑based autofill with tokenized or API‑based authentication; require vendors to provide non‑interactive delegation options.
• Track: Keep a register of exceptions and plan to remove them within a defined timeframe once an approved vendor update is available.

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Final assessment: necessary friction​

This is a textbook case of security hardening that imposes short‑term friction for a measurable reduction in attack surface. The credential UI hardening responds to a concrete privilege‑assignment weakness in Windows Hello (CVE‑2026‑20804) and to a more general class of untrusted input attacks against high‑value authentication UI. From the standpoint of reducing credential theft and tampering risks, the change is well‑justified. From the standpoint of IT operations and helpdesks, it forces a modernization of remote support patterns and automation practices.
The sensible path forward is clear: treat elevation as an emergency, temporary bandage; pressure vendors to update remote tools to use supported credential APIs or delegated tokens; and re‑engineer automation and provisioning to avoid interactive password typing wherever possible. The transition will take effort, but the resulting posture will be more resilient: fewer credential leaks, fewer brittle automation dependencies, and a Windows platform whose protected UI surfaces are less susceptible to remote or programmatic tampering.

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Conclusion
Microsoft’s change to credential autofill is an unwelcome but responsible piece of platform hardening: it breaks legacy conveniences that relied on simulated input, but it materially reduces the attack surface around the most sensitive UI in Windows. Organizations should act deliberately: inventory and test affected workflows, apply short‑term mitigations only with strict controls, and accelerate migration to modern, non‑interactive authentication and delegation models. The long‑term benefit — fewer leaked credentials and stronger integrity of the sign‑in surface — is worth the temporary pain.

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Source: Neowin Microsoft blocks a way for user sign-in on Windows 11 25H2 24H2, and for good reason

 

[ChatGPT]

Microsoft's January security hardening that silently broke credential autofill has sharpened a long‑needed line in the sand: Windows sign‑in dialogs will now ignore untrusted, injected input — and that breakage, while inconvenient, is an intentional defense against a real Windows Hello privilege‑assignment flaw disclosed in mid‑January 2026.

Background / Overview​

On January 13, 2026, Microsoft shipped Patch Tuesday updates that included an explicit behavior change labeled Credentials autofill in the release notes for the January security rollup (notably KB5074109 for recent Windows 11 builds and companion updates). The update introduced a platform hardening: credential dialogs no longer respond to virtual keyboard input from remote desktop or screen‑sharing tools or apps, and certain automated authentication workflows that relied on synthetic keystrokes can fail.
That change is not a bug. It was put in place to address an incorrect privilege assignment in Windows Hello that could be abused to tamper with authentication UI locally. The vulnerability was cataloged as CVE‑2026‑20804 and prompted Microsoft to restrict how the Windows credential user interface (CredUI and sign‑in dialogs) accepts input. The company followed the initial roll‑out with targeted out‑of‑band updates to address regressions in remote sign‑in flows a few days later.
The practical result for many organizations is immediate: legacy remote support patterns — where a technician types or pastes a password on behalf of a user through a screen‑share or remote desktop virtual keyboard — may no longer work. Likewise, scripted automation that fakes keyboard input into protected sign‑in boxes will fail until the automation is redesigned to use supported, delegated authentication mechanisms.

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What changed, exactly? A technical breakdown​

Trusted local input only​

After the January 13 updates, Windows authentication dialogs only accept input from trusted local sources. Microsoft regards the following as trusted:

• Physical keyboards attached to the local endpoint (the interactive user).
• Accessibility tools that hold the UIAccess privilege and meet Windows’ strict requirements (signed, installed in secure system locations).
• Applications running with elevated (administrator/high) integrity.

Input that does not meet those properties — for example, keystrokes injected by a remote screen‑sharing client, a virtual keyboard running inside a remote desktop session, or a script that synthesizes keyboard events — will typically be ignored by the credential UI.

Why this matters from a security perspective​

Credential dialogs are among the highest‑value UI surfaces on Windows. If a malicious or compromised process can programmatically inject keystrokes into a sign‑in box, that vector can be used to capture, replay, or tamper with credentials. The hardening removes a class of remote- and programmatic‑input threats by enforcing tighter input provenance for those dialogs.
The change was driven by an identified Windows Hello weakness in privilege assignment. The underlying flaw allowed local tampering with authentication components in ways that elevated the risk posed by input injection techniques. Microsoft responded by narrowing the set of sources allowed to interact with credential prompts.

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The operational fallout: who will see problems​

Immediate, visible impacts​

• Helpdesk and remote support teams that routinely type or paste passwords into a locked screen or sign‑in dialog via screen share or remote control will suddenly see those actions fail.
• Some Remote Desktop client scenarios and cloud PC flows (Windows App, Azure Virtual Desktop, Windows 365) experienced authentication failures until Microsoft released follow‑up fixes.
• RMM (remote monitoring and management) tools, automation scripts, and test harnesses that relied on synthesizing keystrokes for unattended credential entry can stall or fail.
• Virtual keyboards provided by remote‑control or meeting apps — often used for accessibility or convenience in remote sessions — may stop working when targeted at Windows’ credential UI.

Less likely to be affected​

• Applications that integrate with the platform via official credential APIs (the system credential UI, credential providers, or proper Windows security APIs) generally remain functional.
• Non‑interactive authentication methods — Windows Hello biometrics, smart cards, token‑based flows, and delegated token exchanges — are not targeted by this input‑filtering change when implemented using supported platform mechanisms.

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Timeline and the Microsoft response​

• January 13, 2026: Microsoft published the January security updates and release notes that documented the new Credentials autofill behavior in KB release notes for affected builds.
• In the days following the rollout, administrators reported sign‑in failures in certain remote scenarios. Microsoft issued one or more out‑of‑band cumulative updates (for example, an update rolled on January 17, 2026) that addressed specific regressions affecting Remote Desktop and Windows App sign‑in flows while preserving the security hardening.
• The vulnerability motivating the change was registered as CVE‑2026‑20804, describing an incorrect privilege assignment in Windows Hello that could allow local tampering.

This sequence — fix, discover regression, ship targeted remediation — is typical when a security hardening closes a long‑standing operational loophole: the security gain is real, but the platform must also ensure continuity for legitimate remote workflows.

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Short‑term mitigations and their risks​

Microsoft documented a temporary mitigation that restores the previous autofill behavior in controlled circumstances: run the application that performs remote credential submission with elevated (administrator) privileges. Elevated processes are considered trusted by the hardened credential UI and therefore can provide the input the dialog will accept.
Do not apply that mitigation casually. Elevating a remote support or automation process:

• Re‑expands the trusted boundary, increasing exposure if the elevated process is compromised.
• Encourages poor operational hygiene by normalizing running remote management tools with administrative rights.
• Requires tight compensating controls: network segmentation, access‑restricted administrative bastions, multifactor authentication, session auditing, and short-lived elevation.

If you must use elevation as a stopgap, apply it only for the specific process, restrict the scope, and schedule removal as soon as the vendor supplies a supported update or your automations are re‑architected.

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A practical roadmap for IT teams — triage to long‑term remediation​

Immediate triage (within 48 hours)​

• Inventory affected workflows
  Identify every remote support tool, RMM agent, automation script, and batch job that performs interactive credential input by simulating keyboard events.
• Assess impact
  Prioritize items by business criticality: production access, cloud PC connectivity, helpdesk throughput, and unattended provisioning.
• Apply targeted remediations
• If you encounter the Remote Desktop sign‑in regression, deploy Microsoft’s out‑of‑band fix provided for affected builds as a prioritized patch.
• Use the elevation mitigation only where absolutely necessary and under strict controls.
• Communicate
  Notify helpdesk staff that remote typing into sign‑in boxes may fail and describe alternative procedures (local entry by the user, delegated token flows, temporary elevated agent).

Medium term (30–90 days)​

• Refactor automation: Replace scripts that synthesize keystrokes with programmatic calls to platform credential APIs or tokenized service identities.
• Vendor coordination: Contact remote support and RMM vendors for compatibility updates that avoid keystroke injection; demand timelines and test releases.
• Staging and pilots: Validate patched tools and redesigned automation in a lab or pilot ring before enterprise‑wide rollout.

Long term (90+ days)​

• Adopt delegation and tokenization: Move away from interactive password entry for unattended tasks. Use managed identities, service principals, or certificate‑based authentication for automation.
• Embrace modern, passwordless options: Accelerate adoption of passkeys, Windows Hello with hardware protections (TPM, VBS where available), and integrated SSO solutions.
• Harden accessibility integration: If assistive technologies must interact with credential UI, ensure they meet UIAccess requirements (signed, installed in secure locations, manifest flags) rather than relying on simulated input.

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Guidance for vendors and developers​

Vendors whose products rely on keyboard simulation to populate Windows credential dialogs must change course:

• Stop using SendInput, PostMessage, or synthetic keystrokes against protected credential dialogs.
• Use the system credential APIs that interoperate with credential providers and modern authentication flows.
• For legitimate accessibility needs, follow Microsoft’s UIAccess model: sign the binaries, deploy to approved locations, and include the UIAccess manifest flag so the OS can grant the right privileges safely.
• Where interaction with elevated UI is unavoidable, split functionality: create a minimal, well‑audited elevated service that performs necessary privileged tasks and keep the majority of code running at least privilege.

These adjustments are necessary to preserve both usability and security as the platform disallows unreliable trust assumptions.

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Why the hardening is the right long‑term decision​

The change tightens the platform’s posture around sensitive authentication surfaces. Consider the tradeoffs:

• Security wins: The hardening materially reduces a plausible and exploitable class of credential‑capture techniques that depend on remote or programmatic input injection.
• Operational pain: It forces a modernization of remote support and automation workflows that, for too long, relied on brittle, insecure patterns (typing another person’s password over a screen share is convenient — and risky).
• Net effect: Short‑term friction, long‑term resilience. By forcing vendors and IT teams to adopt platform‑supported APIs and delegated authentication, Windows reduces both the number and the severity of opportunities for credential compromise.

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Key recommendations — a checklist for administrators​

• Inventory and map every workflow that uses injected or synthetic keyboard input for authentication.
• Patch promptly: ensure the January 2026 security updates and subsequent out‑of‑band fixes are installed on endpoints, and validate remote sign‑in flows in a pilot ring.
• Communicate with helpdesk staff and users about temporary process changes and expected behavior.
• Avoid blanket elevation: if you use the mitigation to run a tool elevated, do so under tight controls and document every instance.
• Replace keyboard injection with credential APIs, managed identities, or token delegation.
• Engage vendors: hold remote support and automation vendors to a firm timelines for API‑based compatibility.
• Accelerate passwordless strategies where feasible to remove the problem class entirely.

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What to watch next​

• Vendor updates and compatibility patches from remote support and RMM vendors: these will be the immediate path to restoring full functionality without elevating remote tools.
• Enterprise adoption of delegation and tokenized automation patterns. Organizations that treat this as a modernization opportunity will recover productivity faster and reduce future risk.
• Microsoft follow‑ups: expect clarifying guidance, tooling updates, and potentially new management policies that ease migration for large fleets while preserving the hardening.

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Caveats and cautionary notes​

• The mitigation of running remote credential submission apps with elevated privileges does restore prior behavior, but it also reintroduces elevated trust that attackers can abuse if a remote tool or technician workstation is compromised. Treat elevation as a last resort and ensure compensating controls.
• Some media and community reports described transient regressions (for example, Remote Desktop or Windows App sign‑in issues) after the initial hardening; Microsoft issued out‑of‑band cumulative updates to address specific faults while preserving the security posture. Administrators should verify each endpoint’s build number and installed updates before drawing conclusions about behavior on their estate.
• Not every reported symptom in the wild is necessarily caused by the credential‑UI change; unrelated update regressions can appear concurrently. Always confirm the root cause by testing in a controlled environment and by cross‑checking installed KB and build information.

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Final assessment: necessary friction, worthwhile gain​

Security hardening like this is never painless. It breaks conveniences and forces operational work. But the credential dialog is precisely the component that merits high assurance: treat passwords and sign‑in as special — and harden the platform accordingly.
Microsoft’s decision to restrict credential UI input to trusted local sources is a defensive, platform‑level move that reduces a practical attack surface related to Windows Hello privilege handling. The short‑term cost is extra work for IT teams and vendor partners; the long‑term payoff is stronger protection for the most sensitive interface on Windows.
For administrators, the marching orders are straightforward: inventory, communicate, patch, and modernize. Replace brittle keyboard‑injection workflows with supported credential APIs or tokenized delegation. Use elevation only as a carefully controlled bandage. And insist that third‑party remote support and automation vendors ship compatibility updates that respect the new security model.
Security and usability are at odds here, but history shows that platform hardenings that force vendors and operators to adopt secure primitives ultimately produce a more resilient ecosystem. This is one of those moments: temporary pain that moves the industry one step closer to safer, modern authentication patterns.

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Source: Neowin Microsoft blocks a way for user sign-in on Windows 11 25H2 24H2, and for good reason