CVE-2026-77272

## Summary The OAuth 2.0 setup wizard's local callback HTTP server reflects the `error` query parameter directly into an HTML response without any sanitization or encoding. An attacker can craft a malicious callback URL containing JavaScript in the `error` parameter that executes in the victim's browser when the setup wizard is running. The server binds to all network interfaces (`0.0.0.0`), making it accessible from the local network rather than just localhost. ## Details The vulnerability exists in the `CallbackHandler` class in `src/mcp_atlassian/utils/oauth_setup.py`. **Step 1 -- Attacker-controlled input enters unsanitized:** At line 63-66, the `error` query parameter from the URL is read and interpolated into a message string without HTML escaping: ```python # src/mcp_atlassian/utils/oauth_setup.py:63-66 if "error" in params: callback_error = params["error"][0] callback_received = True self._send_response(f"Authorization failed: {callback_error}") ``` **Step 2 -- Unsanitized input is injected into HTML:** At line 124-125 in `_send_response`, the `message` variable (containing the unescaped attacker input) is injected directly into the HTML template via f-string interpolation: ```python # src/mcp_atlassian/utils/oauth_setup.py:124-125 <div class="message {"success" if status == 200 else "error"}"> <p>{message}</p> </div> ``` **Step 3 -- Server listens on all interfaces:** At line 167, the callback server binds to all network interfaces, not just localhost: ```python # src/mcp_atlassian/utils/oauth_setup.py:167 httpd = socketserver.TCPServer(("", port), handler) ``` This means the XSS is exploitable from any machine that can reach the victim's IP on the callback port (default 8080), not just from the local machine. **Step 4 -- No security headers:** The response at line 84-86 sets `Content-type: text/html` but does not include `Content-Security-Policy`, `X-Content-Type-Options`, or `X-XSS-Protection` headers: ```python # src/mcp_a