* feat: add DNS rebinding protection conformance tests
Add a new server conformance scenario to verify that localhost MCP servers
properly validate Host headers to prevent DNS rebinding attacks.
Checks:
- localhost-host-rebinding-rejected: Verifies server returns 403 for
non-localhost Host headers (e.g., evil.example.com)
- localhost-host-valid-accepted: Verifies server accepts requests with
valid localhost Host headers
Also updates the everything-server example to use createMcpExpressApp()
which includes DNS rebinding protection by default.
Closes#103
Co-Authored-By: Claude <noreply@anthropic.com>
* feat: add negative test case for DNS rebinding protection
Add a minimal MCP server that intentionally omits DNS rebinding protection
to serve as a negative test case. This server is expected to FAIL the
dns-rebinding-protection scenario.
Also update README to document the negative test case.
Co-Authored-By: Claude <noreply@anthropic.com>
* fix: accept any 4xx status code for DNS rebinding rejection
Update the DNS rebinding protection test to accept any 4xx status code
as a valid rejection response, not just 403. This accommodates different
HTTP semantics:
- 403 Forbidden: Per MCP spec
- 421 Misdirected Request: RFC 7540 (semantically correct for DNS rebinding)
- Other 4xx: Implementation-specific error codes
* refactor: address PR review comments
- Simplify negative test server (remove event store, sessions)
- Update spec reference URL to security_best_practices
- Clarify scope: localhost servers without HTTPS/auth
- DRY up checks.push using spread operator
- Fix valid host check to require 2xx response
* fix: include error details in catch block
* refactor: simplify negative test server to stateless
* refactor: check both Host and Origin headers for DNS rebinding protection
- Send both Host and Origin headers in test requests so servers checking
either header will pass the conformance test
- Add second spec reference for Origin check (transports#security-warning)
- Update descriptions to mention both Host and Origin headers
- Fix protocol version to 2025-11-25
- Remove unnecessary 'as const' type assertions
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Co-authored-by: Claude <noreply@anthropic.com>
d0b2b4914d