HTTP Bridge Should Bind to Localhost Only

[jojastahl]

Claude Code crafted this issue:

Security Issue: HTTP Bridge Should Bind to Localhost Only

Description

The HTTP Bridge server in src/mcp/http-bridge.ts does not explicitly bind to localhost, which may allow access from other devices on the local network depending on firewall configuration.

Current Implementation

File: src/mcp/http-bridge.ts:87

this.httpServer!.listen(this.port, () => {
  console.log(`VS Code HTTP Bridge running on port ${this.port}`);
  resolve();
});

When no hostname is specified in Node.js http.Server.listen(), the server binds to all network interfaces (0.0.0.0 by default), not just localhost.

Security Impact

Severity: Medium

If the user's firewall allows it, other devices on the local network could potentially:

• Access the HTTP bridge on port 8991
• Execute any of the 25 exposed tools
• Read the entire VSCode workspace source code
• View debugging session data (variables, call stacks)
• Rename symbols and modify files across the workspace
• Evaluate expressions in active debug sessions

The CORS header Access-Control-Allow-Origin: * (line 19) further allows any origin to connect via browser-based requests.

Recommended Fix

Explicitly bind to localhost to ensure the server is only accessible from the local machine:

this.httpServer!.listen(this.port, 'localhost', () => {
  console.log(`VS Code HTTP Bridge running on localhost:${this.port}`);
  resolve();
});

Alternatively, use 127.0.0.1 for IPv4-only binding:

this.httpServer!.listen(this.port, '127.0.0.1', () => {
  console.log(`VS Code HTTP Bridge running on 127.0.0.1:${this.port}`);
  resolve();
});

Additional Considerations

1. CORS Configuration: Consider restricting CORS to localhost origins only, or removing CORS headers entirely since the MCP standalone server uses direct HTTP requests (not browser-based)

2. Authentication: For defense-in-depth, consider adding a simple authentication token that must be provided via environment variable

3. Documentation: Update README to clearly document the security model and trust boundaries

References

• Node.js HTTP Server Documentation: https://nodejs.org/api/http.html#serverlisten
• Similar issue in other projects: Why listening "::" (all IPv6) also get "0.0.0.0"(all IPv4) listened? nodejs/node#9390

Affected Versions

All versions up to and including v0.1.0