Description

PraisonAI: Cross-Origin Agent Execution via Hardcoded Wildcard CORS and Missing Authentication on AGUI Endpoint

Summary

The AGUI endpoint (POST /agui) has no authentication and hardcodes Access-Control-Allow-Origin: * on all responses. Combined with Starlette/FastAPI's Content-Type-agnostic JSON parsing, any website a victim visits can silently trigger arbitrary agent execution against a locally-running AGUI server and read the full response, including tool execution results and potentially sensitive data from the victim's environment.

Details

The vulnerability is a combination of three issues in src/praisonai-agents/praisonaiagents/ui/agui/agui.py:

1. No authentication (line 124-125):

@router.post("/agui")
async def run_agent_agui(run_input: RunAgentInput):

The endpoint accepts any request. RunAgentInput (defined in types.py:159-165) has no auth token, API key, or session validation field. No middleware or dependencies are attached to the router (line 111).

2. Hardcoded wildcard CORS (line 131-141):

return StreamingResponse(
    event_generator(),
    media_type="text/event-stream",
    headers={
        "Cache-Control": "no-cache",
        "Connection": "keep-alive",
        "Access-Control-Allow-Origin": "*",
        "Access-Control-Allow-Methods": "POST, GET, OPTIONS",...
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The Access-Control-Allow-Origin: * header is hardcoded in the library code. Library consumers cannot override this without patching the source.

3. CORS preflight bypass via Starlette's Content-Type-agnostic parsing: Starlette's Request.json() (used internally by FastAPI for Pydantic body models) calls json.loads(await self.body()) without verifying that Content-Type is application/json. A browser POST with Content-Type: text/plain is classified as a CORS "simple request" per the Fetch specification — no preflight OPTIONS request is sent. Since the JSON body is still parsed successfully, the request executes normally.

Attack flow:

Victim runs an AGUI server locally (the documented usage pattern per the class docstring at lines 42-50)

Victim visits an attacker-controlled website

Attacker's JavaScript sends POST to http://localhost:8000/agui with Content-Type: text/plain containing a JSON body — this is a simple request, no preflight

FastAPI parses the JSON body into RunAgentInput, the agent executes with full tool capabilities

The streaming response includes Access-Control-Allow-Origin: *, so the browser permits the attacker's JavaScript to read the response

Attacker exfiltrates the agent's output, including any tool execution results

PoC

Prerequisites: A locally running AGUI server (the default setup from documentation):

# server.py - standard AGUI setup
from praisonaiagents import Agent
from praisonaiagents.ui.agui import AGUI
from fastapi import FastAPI
import uvicorn

agent = Agent(name="Assistant", role="Helper", goal="Help users")
agui = AGUI(agent=agent)...
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Exploit (runs on any website the victim visits):

<script>
// Simple request - no CORS preflight with text/plain
fetch('http://localhost:8000/agui', {
  method: 'POST',
  headers: {'Content-Type': 'text/plain'},
  body: JSON.stringify({
    thread_id: 'attack-thread',
    messages: [{...
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Expected result: The agent executes the attacker's prompt with whatever tools are configured (file access, code execution, API calls), and the full streamed response is readable by the attacker's JavaScript due to the wildcard CORS header.

Impact

Remote code/tool execution: Any website can trigger agent execution on a victim's local machine with the full permissions of the server process and all configured agent tools

Data exfiltration: Agent responses (including tool outputs like file contents, command results, API responses) are readable cross-origin due to the wildcard CORS header

No user awareness: The attack is silent — no browser prompts, no visible indicators. The victim only needs to have the AGUI server running and visit a malicious page

Blast radius: Impact depends on the agent's configured tools but can include filesystem access, environment variable exposure, network requests from the victim's machine, and arbitrary code execution if code-execution tools are enabled

Recommended Fix

1. Remove the hardcoded wildcard CORS headers and make CORS configurable:

def __init__(
    self,
    agent: Optional["Agent"] = None,
    agents: Optional["Agents"] = None,
    name: Optional[str] = None,
    description: Optional[str] = None,
    prefix: str = "",
    tags: Optional[List[str]] = None,...
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2. Remove CORS headers from the StreamingResponse and let consumers configure CORS via FastAPI's CORSMiddleware with specific origins:

return StreamingResponse(
    event_generator(),
    media_type="text/event-stream",
    headers={
        "Cache-Control": "no-cache",
        "Connection": "keep-alive",
    },
)...
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3. Add a Content-Type check as defense-in-depth to prevent simple-request CORS bypass:

from fastapi import Request, HTTPException

@router.post("/agui")
async def run_agent_agui(request: Request, run_input: RunAgentInput):
    content_type = request.headers.get("content-type", "")
    if "application/json" not in content_type:
        raise HTTPException(status_code=415, detail="Content-Type must be application/json")
    # ... rest of handler...
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4. Add authentication support (e.g., an API key or bearer token dependency on the router) so that cross-origin requests without valid credentials are rejected.

Mitigation

Aliases

References