Cursor AI has rapidly become the go-to code editor for developers worldwide, integrating LLMs directly into the development workflow. However, many users—especially those behind restrictive firewalls or using complex network environments—frequently encounter the dreaded "Connection Failed" error. This issue often stems from Cursor's inability to respect standard system proxy settings, leading to timeouts when trying to reach Anthropic, OpenAI, or Cursor's own backend servers.

In this guide, we will explore why these connection issues occur and how to use Clash (specifically Clash Verge Rev) to resolve them permanently. By leveraging TUN Mode, we can force Cursor AI's traffic through a secure proxy at the network interface level, bypassing the limitations of traditional HTTP proxy settings. Let's get your AI coding environment back on track for 2026.

Why Cursor AI Fails to Connect

The "Connection Failed" error in Cursor is rarely a problem with the software itself. Instead, it is usually a network routing conflict. Here are the primary reasons why Cursor AI struggles with standard proxies:

  • Hardcoded Network Calls: Unlike standard browsers, some components of the Cursor editor (which is based on VS Code) might bypass the Windows proxy registry keys or the HTTP_PROXY environment variables.
  • WebSocket Restrictions: Cursor relies heavily on WebSockets for real-time AI suggestions. Many basic proxy setups fail to handle persistent WebSocket connections correctly over SSL.
  • DNS Pollution: If your local DNS is returning incorrect IP addresses for Cursor’s API endpoints, the connection will fail before it even reaches your proxy.
  • TLS Fingerprinting: Some advanced firewalls detect the specific TLS handshake used by AI tools and drop the packets.

Standard "System Proxy" mode in Clash often isn't enough because it only tells the OS to suggest a proxy to applications. To fix this, we need a more aggressive approach: TUN Mode.

Prerequisites for the Fix

Before moving to the technical steps, ensure you have the following ready:

  1. Clash Verge Rev Installed: This is currently the most stable and feature-rich Clash client for Windows and macOS. You can get it from our download page.
  2. Premium Subscription: Ensure your proxy provider supports high-speed nodes and has stable access to AI services (OpenAI/Anthropic).
  3. Admin Privileges: Enabling TUN mode requires installing a virtual network driver, which requires administrator rights on your computer.

Ensure you have closed Cursor AI completely before starting the configuration to prevent cached connection errors from persisting.

Step 1: Configuring Clash Verge Rev for Cursor

The first step is ensuring Clash is running with the Mihomo (Clash Meta) core, as it provides the best support for modern AI protocols and TUN mode features.

Switching to Mihomo Core

Open Clash Verge Rev, go to Settings, and find the Clash Core section. Ensure that "Mihomo" is selected. If it asks to download, allow it and restart the client. The Mihomo core is essential because it supports process-name based routing and superior DNS hijacking, which are critical for Cursor AI.

Importing AI-Optimized Nodes

Go to the Profiles tab and import your subscription. Once imported, right-click the profile and select Edit. You want to ensure your rules are set up to proxy cursor.sh and anthropic.com. If you are unsure, you can use Global Mode temporarily during the troubleshooting phase.

// Example rule addition for your config
rules:
  - DOMAIN-SUFFIX,cursor.sh,Proxy
  - DOMAIN-SUFFIX,anthropic.com,Proxy
  - DOMAIN-SUFFIX,openai.com,Proxy

Step 2: Activating TUN Mode

TUN mode creates a virtual network card that intercepts all traffic from your machine, regardless of whether the application "wants" to use a proxy or not. This is the ultimate solution for Cursor AI.

1

Install Service Mode — In Clash Verge Rev, go to Settings and find "Service Mode". Click the Install button. You will see a small shield icon turn green when successful. This allows Clash to manage network interfaces.

2

Toggle TUN Mode — Switch the TUN Mode toggle to "On". You might see a Windows prompt asking to allow the new network connection. Click Yes.

3

Verify Interface — Open your terminal and type ipconfig (Windows) or ifconfig (Mac). You should see a new adapter named Meta or clash with an IP like 198.18.0.1.

If TUN mode fails to start, try running Clash Verge Rev as an Administrator by right-clicking the desktop icon.

Step 3: Solving DNS Pollution for Cursor

Even with TUN mode, Cursor might fail if it's trying to connect to a "poisoned" IP address cached by your local DNS. We need to configure Clash to handle DNS queries directly.

In your Clash Verge configuration, ensure the dns section is enabled and enhanced-mode is set to fake-ip. This ensures that when Cursor asks for the IP of api.cursor.sh, Clash gives it a "fake" internal IP immediately, allowing Clash to resolve the real IP through the proxy tunnel later.

dns:
  enable: true
  enhanced-mode: fake-ip
  nameserver:
    - 8.8.8.8
    - 1.1.1.1
  fallback:
    - https://dns.google/dns-query

Advanced Troubleshooting

If you've enabled TUN mode and Cursor AI still shows "Connection Failed", consider these advanced steps:

1. Set Environment Variables

Force Cursor's underlying Electron process to recognize the proxy by setting system-wide environment variables. In Windows Search, type "Environment Variables" and add:

  • HTTP_PROXY: http://127.0.0.1:7897
  • HTTPS_PROXY: http://127.0.0.1:7897

(Note: 7897 is the default port for Clash Verge Rev; check your settings if you changed it).

2. Testing with Global Mode

Switch Clash to Global Mode and select a high-quality US or Singapore node. If Cursor works in Global but not in Rule mode, your rule set is missing Cursor-specific domains. You should update your subscription or add custom rules as shown in Step 1.

3. Firewall Conflicts

Sometimes third-party antivirus software or the Windows Firewall blocks the TUN adapter. Temporarily disable your firewall to see if connectivity returns. If it does, add an exception for the Clash Verge.exe and the mihomo.exe core.

FAQ: Cursor AI & Clash

Does TUN mode slow down my internet?

TUN mode introduces a very slight overhead because it processes every packet at the network layer. However, on modern CPUs, this is unnoticeable. The benefit of having all apps (including terminal, Docker, and Cursor) proxied correctly far outweighs the minor latency.

Why does Cursor work on my browser but not in the app?

Browsers have their own proxy management systems that are very mature. Cursor is a standalone Electron application that manages its own network stack, which is often less flexible and more prone to ignoring system-level proxy configurations.

Can I use Clash for Android to proxy Cursor via Hotspot?

Yes, if you use your Android phone as a hotspot and enable "Allow LAN" in Clash for Android, you can route your PC's traffic through the phone. However, for a stable coding experience, a local installation of Clash Verge is recommended.

Get Started with a Stable Connection

In 2026, AI-assisted coding is no longer a luxury—it's a necessity for high-velocity development. Don't let network configuration issues slow down your creative process. By using a robust tool like Clash Verge Rev and properly configuring TUN mode, you can ensure that Cursor AI remains connected and responsive, regardless of your local network restrictions. For the best performance, always keep your Clash client and Mihomo core updated to the latest versions. Ready to optimize your setup? Visit the Clash client download page to get the latest stable builds for free.