Microsoft Confirms Windows 11 Updates Breaking Enterprise VPN Connections in WSL

Microsoft has acknowledged that recent Windows 11 security updates are causing VPN networking failures for enterprise users running Windows Subsystem for Linux (WSL). The issue affects users who installed the KB5067036 October 2025 non-security update, released October 28th, or any subsequent updates including the KB5072033 cumulative update released during this month's Patch Tuesday.

On impacted systems, users are experiencing connectivity issues with third-party VPN applications when mirrored mode networking is enabled, preventing access to corporate resources. This represents a significant disruption for enterprise development teams who rely on WSL for their Linux-based workflows while connected to corporate networks.

What's Affected: VPN Applications and WSL Mirrored Mode

The problem specifically impacts users running WSL with mirrored mode networking enabled. This networking mode, introduced in September 2023, was designed to improve VPN compatibility by mirroring the Windows host's network configuration into the Linux environment. Ironically, the feature created to solve VPN problems is now at the center of this connectivity issue.

According to Microsoft's documentation, the affected VPN solutions include:

OpenVPN: The widely-used open-source VPN protocol and client software used by many enterprise and personal VPN solutions

Cisco Secure Client (formerly Cisco AnyConnect): One of the most common enterprise VPN solutions used by large organizations worldwide

DirectAccess: Microsoft's own always-on VPN solution for enterprise Windows environments

Microsoft notes that home users running Windows Home or Pro editions are unlikely to experience this issue, as it primarily affects connectivity to enterprise resources over VPN. However, any developer or power user running WSL with mirrored networking and a VPN should be aware of the potential impact.

Technical Details: ARP Request Failures

The root cause of this issue lies in how VPN applications' virtual network interfaces handle Address Resolution Protocol (ARP) requests after the Windows updates are applied. ARP is a fundamental networking protocol that maps IP addresses to MAC (Media Access Control) addresses, enabling devices on a network to discover and communicate with each other.

According to Microsoft: "This issue happens because the VPN application's virtual interface doesn't respond to ARP (Address Resolution Protocol) requests."

When ARP requests go unanswered, the WSL environment cannot properly resolve the IP addresses of resources on the corporate network, effectively breaking network connectivity. Users affected by this bug are seeing "No route to host" errors in their WSL environments, even though their Windows host systems can access the same network destinations without any problems.

This creates a frustrating scenario for developers: their Windows applications work fine, but any Linux-based tools, containers, or development environments running in WSL lose connectivity to corporate resources. For teams relying on WSL for Docker containers, development servers, or Linux-native toolchains, this can bring productivity to a standstill.

Symptoms: How to Identify If You're Affected

If you're experiencing this issue, you'll likely notice the following symptoms:

1. "No route to host" errors: Network commands in WSL fail with routing errors when VPN is connected

2. Windows works, WSL doesn't: The same corporate resources are accessible from Windows browsers and applications but unreachable from within WSL

3. Mirrored networking enabled: The issue only occurs when networkingMode=mirrored is set in your .wslconfig file

4. Recent Windows updates installed: KB5067036 (October 2025) or KB5072033 (December 2025) or later updates are present

To check if mirrored mode is enabled, look for the following in your %USERPROFILE%\.wslconfig file:

[wsl2] networkingMode=mirrored

Background: WSL and Mirrored Mode Networking

Windows Subsystem for Linux was first introduced in March 2016 as a compatibility layer enabling users to run Linux distributions natively on Windows. The original WSL 1 used a translation layer to convert Linux system calls to Windows equivalents, which worked but had significant limitations.

In May 2019, Microsoft released WSL 2, a major architectural overhaul that included a real Linux kernel running in a lightweight virtual machine. This brought dramatic improvements in file system performance, full system call compatibility, and better support for Linux applications. WSL 2 quickly became the preferred option for developers working with Docker, Kubernetes, and Linux-native development tools.

However, WSL 2's virtual machine architecture introduced networking challenges. By default, WSL 2 uses NAT (Network Address Translation) networking, which created complications for VPN connectivity, accessing WSL services from the Windows host, and certain enterprise network configurations.

Mirrored mode networking was introduced in September 2023 specifically to address these VPN compatibility issues. When enabled, it mirrors the Windows host's network configuration into WSL, providing:

• Improved VPN compatibility: Corporate VPN connections work seamlessly with WSL

• IPv6 support: Full IPv6 networking capabilities within WSL

• Multicast support: Required for certain discovery protocols and services

• LAN connectivity: Ability to connect to WSL from other devices on the local network

At Microsoft Build 2025, Microsoft took another major step by open-sourcing WSL, making its source code available on GitHub (except for components that are part of Windows itself). This move was celebrated by the developer community as it allows for greater transparency and community contributions to the platform.

Enterprise Impact: Development Teams Hit Hardest

The timing of this bug is particularly problematic for enterprise development teams. WSL has become a critical tool for developers who need to work with Linux-based technologies while running Windows as their primary operating system. Common use cases affected by this bug include:

Docker and container development: Docker Desktop relies heavily on WSL 2, and container images often need to pull from internal registries accessible only via VPN

Internal Git repositories: Many enterprises host their source code on internal GitLab, Bitbucket, or GitHub Enterprise servers that require VPN access

Database access: Development and staging databases often reside on corporate networks protected by VPN

Internal APIs and services: Microservices architectures typically involve numerous internal endpoints that become unreachable

Package managers and artifacts: Internal npm, Maven, or pip repositories used for dependency management

For organizations with strict security policies requiring VPN connections for all corporate resource access, this bug effectively makes WSL unusable for work purposes until a fix is deployed.

Current Status: No Fix or Official Workaround Yet

Microsoft has confirmed the issue as a known bug and says it is actively investigating, but has not yet provided a timeline for a fix or an official workaround. The company states that "additional information would be shared when available."

In the meantime, affected users have limited options:

Disable mirrored mode: Remove or comment out the networkingMode=mirrored line in .wslconfig. This reverts to NAT networking, which may restore basic connectivity but sacrifices the VPN compatibility benefits that mirrored mode was designed to provide.

Roll back updates: Uninstall KB5067036 and KB5072033 if your organization's security policy permits. This is generally not recommended as it removes important security patches.

Use traditional virtual machines: As a temporary measure, some teams are reverting to full Linux VMs using Hyper-V or VMware, which adds overhead but maintains VPN connectivity.

Wait for a patch: Microsoft typically addresses high-impact known issues in subsequent cumulative updates or out-of-band patches for severe problems.

Recommendations for IT Administrators

IT administrators managing enterprise Windows deployments should consider the following steps:

1. Assess WSL usage: Identify which development teams or users rely on WSL with mirrored networking enabled

2. Communicate the issue: Proactively inform affected teams about the known issue and potential workarounds

3. Test before deploying: If you haven't deployed KB5072033 yet, test it in a controlled environment with your VPN solution first

4. Monitor Microsoft's release health dashboard: Watch for updates on this known issue and any forthcoming fixes

5. Prepare alternative workflows: Have fallback options ready for critical teams who cannot wait for an official fix

This incident highlights the complex interdependencies in modern Windows networking, particularly when virtualization, VPNs, and enterprise security tools must all coexist. While mirrored mode networking was a welcome addition to WSL, the interaction with VPN virtual network interfaces proves to be a fragile point of integration.

We will update this article when Microsoft releases additional information or a fix for this issue. In the meantime, affected users should monitor the Windows release health dashboard and consider the temporary workarounds described above.

Learn More

For more information on the security concepts mentioned in this article, see our Learn section for guides on VPN fundamentals and enterprise networking security best practices.