CVE-2025-26635: Windows 10 1809 Auth Bypass Vulnerability

CVE-2025-26635 Overview

CVE-2025-26635 is a weak authentication vulnerability in Windows Hello that allows an authorized attacker to bypass a security feature over a network. Windows Hello is Microsoft's biometric authentication system that provides passwordless sign-in capabilities using facial recognition, fingerprint scanning, or PIN authentication. This vulnerability represents a significant security concern as it undermines the fundamental authentication protections that Windows Hello is designed to provide.

The vulnerability stems from weak authentication mechanisms (CWE-1390) within the Windows Hello component, allowing attackers with elevated privileges to circumvent security features designed to protect user authentication processes.

Critical Impact
Authorized attackers can bypass Windows Hello security features over a network, potentially compromising authentication integrity and gaining unauthorized access to protected resources.

Affected Products

Microsoft Windows 10 1809 (x64 and x86)
Microsoft Windows 10 21H2
Microsoft Windows 10 22H2
Microsoft Windows 11 22H2 (x64 and ARM64)
Microsoft Windows 11 23H2 (x64 and ARM64)
Microsoft Windows Server 2019
Microsoft Windows Server 2022
Microsoft Windows Server 2022 23H2

Discovery Timeline

April 8, 2025 - CVE-2025-26635 published to NVD
July 3, 2025 - Last updated in NVD database

Technical Details for CVE-2025-26635

Vulnerability Analysis

This vulnerability is classified under CWE-1390 (Weak Authentication), indicating a fundamental flaw in how Windows Hello validates authentication requests over network connections. The weakness allows authenticated attackers with high privileges to bypass security features that should otherwise prevent unauthorized access.

The attack requires network access and high-level privileges but does not require user interaction, making it exploitable in scenarios where an attacker has already gained some level of access to the network or system. The impact is primarily on confidentiality and integrity, with no direct availability impact reported.

Root Cause

The root cause of CVE-2025-26635 lies in the weak authentication implementation within Windows Hello's network-facing authentication components. The system fails to properly validate authentication requests in certain network scenarios, allowing attackers with elevated privileges to bypass the intended security controls. This weakness in the authentication chain means that the biometric or PIN-based protections can be circumvented through network-based attack vectors.

Attack Vector

The vulnerability is exploitable over a network by an attacker who already possesses high-level privileges on the target system or network. The attack does not require user interaction, allowing for potential automated exploitation. An attacker would need to:

Gain authenticated access to the target network or system with elevated privileges
Target the Windows Hello authentication mechanism through network-based requests
Exploit the weak authentication validation to bypass security features
Potentially gain access to resources protected by Windows Hello authentication

Since no verified proof-of-concept code is publicly available and this vulnerability has not been observed in active exploitation, technical details regarding specific exploitation methods are limited. For detailed technical information, refer to the Microsoft Security Update Guide.

Detection Methods for CVE-2025-26635

Indicators of Compromise

Unusual authentication events in Windows Hello logs indicating bypassed verification steps
Anomalous network authentication requests targeting Windows Hello services
Unexpected access to resources that should require Windows Hello authentication
Authentication success events without corresponding biometric or PIN validation

Detection Strategies

Monitor Windows Security Event Logs for unusual authentication patterns related to Windows Hello (Event IDs 4624, 4625, 4648)
Implement network monitoring to detect anomalous authentication traffic targeting Windows Hello services
Deploy endpoint detection solutions to identify suspicious authentication bypass attempts
Review credential provider logs for signs of authentication mechanism tampering

Monitoring Recommendations

Enable verbose logging for Windows Hello authentication events
Configure SIEM rules to alert on authentication anomalies involving Windows Hello
Monitor for privilege escalation attempts that may precede exploitation of this vulnerability
Implement behavioral analytics to detect deviations from normal authentication patterns

How to Mitigate CVE-2025-26635

Immediate Actions Required

Apply the latest Microsoft security updates for all affected Windows versions immediately
Review and restrict network access to systems using Windows Hello authentication
Audit accounts with high privileges that could potentially exploit this vulnerability
Implement additional authentication layers as defense-in-depth measures

Patch Information

Microsoft has released security updates to address CVE-2025-26635. Organizations should apply the appropriate patches for their Windows versions as soon as possible. Detailed patch information and download links are available in the Microsoft Security Update Guide for CVE-2025-26635.

The following systems require patching:

Windows 10 versions: 1809, 21H2, 22H2
Windows 11 versions: 22H2, 23H2
Windows Server versions: 2019, 2022, 2022 23H2

Workarounds

Restrict network access to Windows Hello authentication services using firewall rules
Implement network segmentation to limit exposure of systems relying on Windows Hello
Consider temporarily disabling Windows Hello in high-security environments until patches can be applied
Enforce multi-factor authentication as an additional security layer alongside Windows Hello

bash

# Check Windows Hello status via PowerShell
Get-WinUserAuthenticationProvider

# Review Windows Hello configuration
dsregcmd /status

# Verify current Windows version and patch level
winver
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