fix: validate Origin header on WebSocket upgrade to prevent cross-site WebSocket hijacking

[sebastiondev]

Vulnerability Summary

Type: Cross-Site WebSocket Hijacking (CSWSH)
CWE: CWE-346: Origin Validation Error
Severity: High
File: mcp-bridge/src/daemon.ts

Data Flow

The MCP daemon starts an HTTP server on 127.0.0.1:9223 and upgrades connections to WebSocket on three paths (/extension, /bridge, /cli). All three paths go through a single httpServer.on("upgrade", ...) handler. The handler does not validate the Origin header before completing the WebSocket handshake.

Because the server is bound to 127.0.0.1, it is reachable from any JavaScript running in the user's browser. Browsers always attach an Origin header on WebSocket connections initiated from web pages, and JavaScript cannot spoof this header. Without origin validation, any malicious web page can establish a WebSocket connection to the daemon and invoke the full AIPex tool suite.

Exploit Scenario

A user with the AIPex daemon running visits a malicious (or ad-compromised) web page. The page connects to ws://127.0.0.1:9223/bridge and gains access to ~30+ MCP tools including:

• create_new_tab — open phishing pages
• capture_screenshot — exfiltrate visual data
• download_text_as_markdown — exfiltrate page content
• execute_skill_script — run arbitrary skill scripts
• computer — simulate mouse/keyboard input

// Example CSWSH exploit
const ws = new WebSocket("ws://127.0.0.1:9223/bridge");
ws.onopen = () => {
  ws.send(JSON.stringify({
    jsonrpc: "2.0", id: 1, method: "tools/call",
    params: { name: "create_new_tab", arguments: { url: "http://evil.com/phishing" } }
  }));
};

Preconditions (all highly realistic for any AIPex user)

1. AIPex MCP daemon is running (auto-starts with MCP bridge)
2. AIPex Chrome extension is connected
3. User visits any malicious web page
4. Daemon is on default port 9223

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Fix Description

1 file changed, 39 insertions, purely additive — no existing behavior modified.

The fix adds an isOriginAllowed() function and an origin check at the single chokepoint — the httpServer.on("upgrade") handler, which is the sole entry point for all three WebSocket paths.

Allowed origins:

Origin	Client	Rationale
undefined (no header)	Node.js clients (bridge.ts, cli.ts, aipex-cli)	Node.js ws library does not send Origin
chrome-extension://...	AIPex Chrome extension	Trusted local extension
moz-extension://...	Firefox extension equivalent	Future-proofing for Firefox support

Rejected origins:

Origin	Source	Rationale
http://... / https://...	Web pages in browser	CSWSH attack vector

Rejected connections receive HTTP/1.1 403 Forbidden and the socket is destroyed immediately — before the WebSocket handshake completes.

Rationale

• Single chokepoint: All WebSocket upgrades flow through one handler. The fix intercepts here, so there are no parallel bypass paths.
• Browser-enforced security property: Browsers always send Origin on WebSocket connections from web pages, and JavaScript cannot forge it. This makes origin checking a reliable defense.
• No functional impact: Legitimate clients (Node.js processes and the Chrome extension) are explicitly allowed.

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Test Results

14 tests were designed and validated covering:

Category	Tests	Result
Allowed origins (no header, chrome-extension://, moz-extension://)	3	✅ Pass
Blocked origins (http, https, null, empty, custom schemes)	7	✅ Pass
Edge cases (case sensitivity, trailing slashes, substrings)	4	✅ Pass

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Disprove Analysis

We systematically attempted to disprove or downgrade this finding:

Could authentication protect against this?

No. grep for auth-related patterns returned zero results in daemon.ts. All WebSocket endpoints are completely unauthenticated.

Does localhost binding mitigate this?

Partially. It prevents remote network access, but CSWSH is a browser-based attack that originates from 127.0.0.1 (the browser process). Localhost binding does not protect against it.

Are there other mitigations?

None found. No CORS headers, no token-based validation, no input validation, no rate limiting.

Could there be bypass paths around the fix?

No. All three WebSocketServer instances (extensionWss, bridgeWss, cliWss) use { noServer: true }, meaning the single upgrade handler is the sole entry point. The /health HTTP endpoint only returns status info and is CORS-blocked by browsers from cross-origin reads.

Is this a known issue?

No prior security issues in the repository's issue tracker. No SECURITY.md found.

Prior art

CSWSH against localhost WebSocket servers is a well-documented attack class:

• CVE-2018-1000559 (WebSocket origin bypass)
• CVE-2015-6938 (Jupyter Notebook WebSocket CSWSH)
• OWASP documents this under "Cross-Site WebSocket Hijacking"
• The ws library documentation itself recommends origin validation when using { noServer: true }

CWE Classification Note

The initial finding was tagged CWE-319 (Cleartext Transmission). CWE-346 (Origin Validation Error) is a more precise classification for CSWSH. The vulnerability and fix remain the same regardless.

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Verdict

CONFIRMED VALID — High confidence. The fix is clean (39 lines), correct (single chokepoint, no bypasses), purely additive, and addresses a real, exploitable vulnerability with high impact. No existing tests or functionality are affected.

Thank you for your time reviewing this. Happy to discuss or adjust anything.

[buttercannfly]

Thanks @sebastiondev , really helpful commit