CORS Anywhere

CORS Anywhere is a NodeJS proxy which adds CORS headers to the proxied request.

The url to proxy is literally taken from the path, validated and proxied. The protocol part of the proxied URI is optional, and defaults to "http". If port 443 is specified, the protocol defaults to "https".

This package does not put any restrictions on the http methods or headers, except for cookies. Requesting user credentials is disallowed. The app can be configured to require a header for proxying a request, for example to avoid a direct visit from the browser.

⚠️ Important: See docs/SECURITY.md for critical security considerations before deploying to production.

Fork Improvements

This fork includes important security and quality updates:

Security & Dependencies:

• ✅ Zero vulnerabilities - Fixed all 5 npm audit issues
• 🔒 Upgraded http-proxy 1.11.1 → 1.18.1 (CVE-2024-21501 DoS fix)
• 🧪 Added comprehensive security test suite (test/test-security.js)

Memory Leak Fixes:

• 🔧 Fixed rate limiter setInterval leak (added destroy method for cleanup)
• 🧹 Added help file cache size limit (prevents unbounded growth)
• 🗑️ Cleanup request state in error handler (prevents state accumulation)

Testing & Quality:

• ✅ 137/137 tests passing (functionality, security, memory, rate-limiting)
• 📦 Modern dependencies: mocha v10.7.3, nock v13.5.5, supertest v7.0.0, eslint v8.57.0
• 🔧 Node.js: v0.10+ (library), v14+ (development), tested on v14-v22

Documentation:

• 📚 docs/SECURITY.md - Production hardening guide
• 📝 docs/VULNERABILITY_FIXES.md - Detailed security fixes changelog
• 🤖 .github/copilot-instructions.md - AI contributor guidelines

Compatibility: No breaking API changes. http-proxy 1.18.1 adds x-forwarded-host header automatically.

Example

// Listen on a specific host via the HOST environment variable
var host = process.env.HOST || '0.0.0.0';
// Listen on a specific port via the PORT environment variable
var port = process.env.PORT || 8080;

var cors_proxy = require('cors-anywhere');
cors_proxy.createServer({
    originWhitelist: [], // Allow all origins
    requireHeader: ['origin', 'x-requested-with'],
    removeHeaders: ['cookie', 'cookie2']
}).listen(port, host, function() {
    console.log('Running CORS Anywhere on ' + host + ':' + port);
});

Request examples:

• http://localhost:8080/http://google.com/ - Google.com with CORS headers
• http://localhost:8080/google.com - Same as previous.
• http://localhost:8080/google.com:443 - Proxies https://google.com/
• http://localhost:8080/ - Shows usage text, as defined in lib/help.txt
• http://localhost:8080/favicon.ico - Replies 404 Not found

Live examples:

• https://cors-anywhere.herokuapp.com
• https://robwu.nl/cors-anywhere.html - This demo shows how to use the API.

Documentation

Client

To use the API, just prefix the URL with the API URL. Take a look at demo.html for an example. A concise summary of the documentation is provided at lib/help.txt.

Note: as of February 2021, access to the demo server requires an opt-in, see: https://github.com/Rob--W/cors-anywhere/issues/301

If you want to automatically enable cross-domain requests when needed, use the following snippet:

(function() {
    var cors_api_host = 'cors-anywhere.herokuapp.com';
    var cors_api_url = 'https://' + cors_api_host + '/';
    var slice = [].slice;
    var origin = window.location.protocol + '//' + window.location.host;
    var open = XMLHttpRequest.prototype.open;
    XMLHttpRequest.prototype.open = function() {
        var args = slice.call(arguments);
        var targetOrigin = /^https?:\/\/([^\/]+)/i.exec(args[1]);
        if (targetOrigin && targetOrigin[0].toLowerCase() !== origin &&
            targetOrigin[1] !== cors_api_host) {
            args[1] = cors_api_url + args[1];
        }
        return open.apply(this, args);
    };
})();

If you're using jQuery, you can also use the following code instead of the previous one:

jQuery.ajaxPrefilter(function(options) {
    if (options.crossDomain && jQuery.support.cors) {
        options.url = 'https://cors-anywhere.herokuapp.com/' + options.url;
    }
});

Server

The module exports createServer(options), which creates a server that handles proxy requests. The following options are supported:

• function getProxyForUrl - If set, specifies which intermediate proxy to use for a given URL. If the return value is void, a direct request is sent. The default implementation is proxy-from-env, which respects the standard proxy environment variables (e.g. https_proxy, no_proxy, etc.).
• array of strings originBlacklist - If set, requests whose origin is listed are blocked. Example: ['https://bad.example.com', 'http://bad.example.com']
• array of strings originWhitelist - If set, requests whose origin is not listed are blocked. If this list is empty, all origins are allowed. Example: ['https://good.example.com', 'http://good.example.com']
• function handleInitialRequest - If set, it is called with the request, response and a parsed URL of the requested destination (null if unavailable). If the function returns true, the request will not be handled further. Then the function is responsible for handling the request. This feature can be used to passively monitor requests, for example for logging (return false).
• function checkRateLimit - If set, it is called with the origin (string) of the request. If this function returns a non-empty string, the request is rejected and the string is send to the client.
• boolean redirectSameOrigin - If true, requests to URLs from the same origin will not be proxied but redirected. The primary purpose for this option is to save server resources by delegating the request to the client (since same-origin requests should always succeed, even without proxying).
• array of strings requireHeader - If set, the request must include this header or the API will refuse to proxy. Recommended if you want to prevent users from using the proxy for normal browsing. Example: ['Origin', 'X-Requested-With'].
• array of lowercase strings removeHeaders - Exclude certain headers from being included in the request. Example: ["cookie"]
• dictionary of lowercase strings setHeaders - Set headers for the request (overwrites existing ones). Example: {"x-powered-by": "CORS Anywhere"}
• number corsMaxAge - If set, an Access-Control-Max-Age request header with this value (in seconds) will be added. Example: 600 - Allow CORS preflight request to be cached by the browser for 10 minutes.
• string helpFile - Set the help file (shown at the homepage). Example: "myCustomHelpText.txt"

For advanced users, the following options are also provided.

• httpProxyOptions - Under the hood, http-proxy is used to proxy requests. Use this option if you really need to pass options to http-proxy. The documentation for these options can be found in http-proxy documentation.
• httpsOptions - If set, a https.Server will be created. The given options are passed to the https.createServer method.

For even more advanced usage (building upon CORS Anywhere), see the sample code in test/test-examples.js.

Development

Requirements

• Node.js >= 0.10.0 (library), >= 14.0.0 (development)
• npm

Testing

npm test                # Run all tests (137 tests)
npm run test-coverage   # Run tests with coverage report
npm run lint            # Run ESLint

Dependencies

Production:

• http-proxy ^1.18.1 - HTTP/HTTPS proxy
• proxy-from-env 0.0.1 - Proxy configuration from environment

Development:

• mocha ^10.7.3, nock ^13.5.5, supertest ^7.0.0, eslint ^8.57.0, nyc ^17.1.0, lolex ^6.0.0

Demo server

A public demo of CORS Anywhere is available at https://cors-anywhere.herokuapp.com. This server is only provided so that you can easily and quickly try out CORS Anywhere. To ensure that the service stays available to everyone, the number of requests per period is limited, except for requests from some explicitly whitelisted origins.

Note: as of February 2021, access to the demo server requires an opt-in, see: https://github.com/Rob--W/cors-anywhere/issues/301

If you expect lots of traffic, please host your own instance of CORS Anywhere, and make sure that the CORS Anywhere server only whitelists your site to prevent others from using your instance of CORS Anywhere as an open proxy.

⚠️ Security Warning: See docs/SECURITY.md for critical security considerations. Improper configuration can make your server vulnerable to abuse as an open proxy.

For instance, to run a CORS Anywhere server that accepts any request from some example.com sites on port 8080, use:

export PORT=8080
export CORSANYWHERE_WHITELIST=https://example.com,http://example.com,http://example.com:8080
node server.js

Additional Documentation

• docs/SECURITY.md - Security best practices and hardening guide
• docs/VULNERABILITY_FIXES.md - Security fixes changelog
• .github/copilot-instructions.md - AI coding agent guidelines
• test/test-examples.js - Advanced usage examples

License

This project is licensed under the MIT License - see the LICENSE file for details.