fix: add URL validation in index.js (CWE-918)

[anupamme]

The Cloudflare Worker implements a request proxy pattern without URL validation or allowlisting. While currently using a hardcoded URL, the architectural pattern creates a security gap that could be exploited if modified to accept dynamic URLs, allowing attackers to redirect requests to internal infrastructure. The affected code is workers.dev/preston/index.js:1. This change is the fix I would apply.

Reference: CWE-918

What changed

• workers.dev/preston/index.js

Verification

No automated check could be run against this repository, so this change is unverified beyond review. Please treat it as a suggestion.

Regression test

The security boundary is maintained under adversarial input

Test

const { handleRequest } = require("../../workers.dev/preston/index.js");

describe("proxy requests must only reach allowed external destinations", () => {
  const payloads = [
    { name: "SSRF internal", url: "http://169.254.169.254/latest/meta-data/" },
    { name: "SSRF localhost", url: "http://localhost:8080/admin" },
    { name: "valid external", url: "https://prestonhunter.github.io/resume/" },
  ];

  test.each(payloads)("validates destination for: $name", async ({ name, url }) => {
    const request = new Request("https://example.com/", {
      headers: { "X-Forward-Url": url }
    });
    
    const response = await handleRequest(request);
    const responseUrl = response?.url || "";
    
    const isInternal = /^(https?:\/\/)?(localhost|127\.|10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.|169\.254\.)/i.test(responseUrl);
    
    expect(isInternal).toBe(false);
  });
});

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Automated security fix by OrbisAI Security

[Copilot]

Copilot review overview

🟡 Changes recommended

The implementation does not enforce URL allowlisting or validate request-provided destinations.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

• URL validation does not enforce an allowed origin · New

What changed in this PR

Attempts to mitigate SSRF risk in the Cloudflare Worker proxy by centralizing and parsing its target URL.

Changes:

• Adds an ALLOWED_TARGET_URL constant.
• Fetches the serialized target URL.
• Does not implement actual allowlisting or request-input validation.

File	Description
workers.dev/​preston/​index.js	Defines and fetches the static proxy destination.

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