Vulnerable code sample

import asyncio
import websockets
import threading
import time
import sys

# This code is a conceptual representation of the vulnerability described
# in CVE-2026-34824. It is not the actual source code from the Mesop framework.
# The purpose is to demonstrate the core flaw: spawning an unbounded number of
# threads in response to WebSocket messages.

def resource_consuming_task(message):
    """
    A function that simulates a task that takes time and holds a thread.
    In a real-world scenario, this could be a slow I/O operation or
    a complex computation.
    """
    thread_name = threading.current_thread().name
    print(f"New thread '{thread_name}' started to process message of size {len(message)}.")
    # Keep the thread alive for a while to simulate work and demonstrate
    # how threads can accumulate quickly.
    time.sleep(45)
    print(f"Thread '{thread_name}' finished processing.")


async def vulnerable_websocket_handler(websocket, path):
    """
    This handler contains the vulnerability. For every message received, it
    spawns a new OS thread without any limits.
    """
    client_address = websocket.remote_address
    print(f"Client connected from {client_address}")
    try:
        # Process messages from the client
        async for message in websocket:
            # --- VULNERABILITY ---
            # A new thread is created for every single incoming message.
            # There is no thread pool, queue, or any form of rate limiting.
            # An attacker can send messages in a rapid succession, causing
            # the server to spawn an unbounded number of threads, leading
            # to thread exhaustion and a Denial of Service (DoS).
            print(f"Received message from {client_address}. Spawning a new unmanaged thread.")
            thread = threading.Thread(
                target=resource_consuming_task,
                args=(message,),
                daemon=True # Daemon threads won't block program exit
            )
            thread.start()
            # The server does not wait for the thread to complete and immediately
            # listens for the next message, allowing the attack to proceed rapidly.

    except websockets.exceptions.ConnectionClosed:
        print(f"Client disconnected from {client_address}")
    except Exception as e:
        print(f"An error occurred with client {client_address}: {e}")


async def main():
    """
    Sets up and runs the vulnerable WebSocket server.
    """
    host = "0.0.0.0"
    port = 8765
    print(f"Starting vulnerable WebSocket server on ws://{host}:{port}")
    print("WARNING: This server is designed to demonstrate an uncontrolled resource consumption vulnerability.")
    print("Send rapid WebSocket messages to it to trigger the creation of many threads.")

    server = await websockets.serve(vulnerable_websocket_handler, host, port)

    try:
        await server.wait_closed()
    except asyncio.CancelledError:
        print("Server shutdown initiated.")
        server.close()
        await server.wait_closed()


if __name__ == "__main__":
    try:
        asyncio.run(main())
    except KeyboardInterrupt:
        print("\nServer stopped by user.")
        sys.exit(0)