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ToolsMCPServer Legacy SSE Transport Accepts Attacker Host/Origin and Exposes Registered Tools

High
MervinPraison published GHSA-vmf9-xx9w-86wx Jun 17, 2026

Package

pip praisonai (pip)

Affected versions

>= 3.10.0, <= 4.6.58

Patched versions

>= 4.6.59
pip praisonaiagents (pip)
>= 0.6.0, <= 1.6.58
>= 1.6.59

Description

Summary

praisonaiagents.mcp.ToolsMCPServer.run_sse() builds a Starlette MCP HTTP+SSE server around mcp.server.sse.SseServerTransport. The server exposes /sse and /messages/, but it does not validate Origin, does not validate Host, and does not require any authentication.

This is reachable through supported PraisonAI code paths that wrap configured MCP server tools and re-expose them over legacy SSE:

  • praisonai mcp run <name> --transport sse
  • praisonai serve mcp --name <name> --transport sse
  • direct use of ToolsMCPServer(...).run_sse(...) or launch_tools_mcp_server(..., transport="sse")

A malicious website can use DNS rebinding against a local or internal PraisonAI SSE MCP server and send requests with attacker-controlled Host and Origin headers. the PoV binds only to 127.0.0.1, sends an attacker Host and Origin, lists the registered tool, and invokes it successfully.

The same attacker Origin is rejected by PraisonAI's current Streamable HTTP transport with HTTP 403. The vulnerability is therefore a sibling transport guard gap in the legacy SSE wrapper, not intended behavior.

Technical Details

Current ToolsMCPServer.run_sse() constructs a Starlette app directly:

sse_path = "/sse"
messages_path = "/messages/"
sse_transport = SseServerTransport(messages_path)

async def handle_sse(request: Request):
    async with sse_transport.connect_sse(
        request.scope, request.receive, request._send
    ) as (read_stream, write_stream):
        await mcp._mcp_server.run(
            read_stream,
            write_stream,
            mcp._mcp_server.create_initialization_options()
        )

app = Starlette(
    debug=self._debug,
    routes=[
        Route(sse_path, endpoint=handle_sse),
        Mount(messages_path, app=sse_transport.handle_post_message),
    ]
)

uvicorn.run(app, host=host, port=port)

There is no middleware or route-level check for:

  • Origin
  • Host
  • Authorization
  • API key
  • allowed origins / allowed hosts

The configured CLI wrapper exposes this path:

from praisonaiagents.mcp import MCP, ToolsMCPServer
cmd_string = " ".join(cmd)
mcp = MCP(cmd_string, timeout=60, env=server.env or {})
tools = mcp.get_tools()
mcp_server = ToolsMCPServer(name=name, tools=tools)
mcp_server.run_sse(host=host, port=port)

By contrast, the current Streamable HTTP transport validates Origin and returns HTTP 403 for an invalid origin:

origin = request.headers.get("Origin")
if not self._validate_origin(origin):
    return JSONResponse(..., status_code=403)

Why This Is Not Intended Behavior

This is not only a trust-model disagreement.

PraisonAI's MCP documentation describes Streamable HTTP, WebSocket, and legacy SSE as supported MCP transport mechanisms. The same documentation says the MCP module's security properties include origin validation, authentication headers, and secure session IDs. The transport guide also has a dedicated security section for origin validation as DNS rebinding prevention and authentication.

The official MCP specification warns that HTTP transports need origin validation to prevent DNS rebinding, should bind locally for local servers, and should implement authentication. It also says that without those protections, remote websites can interact with local MCP servers.

The upstream MCP Python SDK advisory GHSA-9h52-p55h-vw2f / CVE-2025-66416 classifies unauthenticated localhost HTTP/SSE MCP servers without DNS rebinding protection as a High severity issue because malicious websites can invoke tools or access resources exposed by the local MCP server. That advisory also says custom low-level SseServerTransport configurations should explicitly configure transport security settings when running unauthenticated localhost servers.

PraisonAI's current Streamable HTTP implementation already enforces an Origin guard and rejects the exact attacker Origin used in the PoV. The issue is that the legacy SSE sibling path lacks the same boundary.

PoV

Run from a local reproduction checkout:

uv run --with mcp --with starlette --with uvicorn --with httpx --with anyio \
  python poc/pov_poc.py \
  --repo-src /path/to/PraisonAI

Observed current-head result:

{
  "http_stream_control": {
    "attacker_origin": "http://attacker.example.test",
    "rejects_attacker_origin": true,
    "status_code": 403,
    "transport": "current_http_stream"
  },
  "source_checks": {
    "has_auth_check": false,
    "has_host_check": false,
    "has_origin_check": false,
    "has_sse_transport": true,
    "route_count": 2
  },
  "sse_probe": {
    "attacker_headers": {
      "Host": "attacker.example.test:62380",
      "Origin": "http://attacker.example.test:62380"
    },
    "bind_host": "127.0.0.1",
    "marker_value": "executed-from-attacker-origin",
    "marker_written": true,
    "server_started": true,
    "tool_call_content": [
      "recorded:executed-from-attacker-origin"
    ],
    "tool_call_error": false,
    "tool_names": [
      "record_marker"
    ],
    "vulnerable": true
  },
  "vulnerable": true
}

The PoV:

  1. imports the current ToolsMCPServer;
  2. registers one marker tool;
  3. monkey-patches uvicorn.run only to capture the exact Starlette app created by run_sse();
  4. starts that app on 127.0.0.1;
  5. connects to /sse with attacker-controlled Host and Origin;
  6. lists tools and calls the marker tool;
  7. runs a control against PraisonAI's current Streamable HTTP transport and confirms the same attacker Origin is rejected with HTTP 403.

PoC

The PoV section above contains the local reproduction command, input, and decisive output.

Impact

If a PraisonAI user starts a local or internal legacy SSE MCP server with registered tools, an attacker who gets that user to visit a malicious website can use DNS rebinding to interact with the SSE server through the browser. The attacker can discover exposed tools and invoke them as the local user.

Impact depends on the configured tools. In realistic PraisonAI MCP deployments, registered tools may access local files, repositories, issue trackers, cloud APIs, internal services, or other automation targets. This can lead to confidentiality, integrity, and availability impact for the resources reachable by the exposed tools.

The PoV is local-only and harmless. It exposes one marker tool that writes a canary string to a temporary directory.

Severity

Suggested severity: High.

Suggested CVSS 3.1:

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

Score: 8.3.

Rationale:

  • AV:N: the attack uses browser-origin HTTP requests to a local/internal service.
  • AC:H: practical exploitation requires DNS rebinding or equivalent browser origin setup.
  • PR:N: no PraisonAI credentials are required by the SSE server.
  • UI:R: the user must visit an attacker-controlled page.
  • S:C: the vulnerable transport exposes tools that operate on resources outside the HTTP transport itself.
  • C/I/A:H: exposed tools may read, mutate, or disrupt local/internal resources depending on the configured MCP server.

Suggested CWEs:

  • CWE-346: Origin Validation Error
  • CWE-306: Missing Authentication for Critical Function
  • CWE-862: Missing Authorization

Suggested Fix

Bring legacy SSE server security in line with the current Streamable HTTP transport, or disable the legacy SSE server path.

Recommended changes:

  1. Add explicit allowed-origin and allowed-host validation to both /sse and /messages/.
  2. Reject invalid Origin with HTTP 403 before opening the SSE stream or accepting POST messages.
  3. Validate Host for local and internal deployments to mitigate DNS rebinding even when browsers omit or vary Origin.
  4. Require authentication for all non-stdio MCP HTTP transports, including SSE.
  5. Add --api-key, --allowed-origins, and --allowed-hosts options to praisonai mcp run and praisonai serve mcp when --transport sse is used.
  6. Where the installed MCP SDK supports it, configure the SDK transport-security settings for low-level SseServerTransport usage instead of mounting it without Host/Origin protection.
  7. Consider deprecating or disabling --transport sse server mode in favor of the current Streamable HTTP implementation.
  8. Add regression tests proving that attacker Host and Origin values are rejected on both /sse and /messages/, and that current Streamable HTTP and legacy SSE enforce the same boundary.

Affected Package/Versions

  • Repository: MervinPraison/PraisonAI
  • Packages:
  • praisonaiagents
  • praisonai
  • Primary component: src/praisonai-agents/praisonaiagents/mcp/mcp_server.py
  • CLI wrappers:
  • src/praisonai/praisonai/cli/commands/mcp.py
  • src/praisonai/praisonai/cli/commands/serve.py
  • Latest verified release/current head:
  • praisonaiagents 1.6.58
  • PraisonAI 4.6.58
  • repo head 1ad58ca02975ff1398efeda694ea2ab78f20cf3e

Suggested affected ranges:

  • praisonaiagents >= 0.6.0, <= 1.6.58
  • praisonai >= 3.10.0, <= 4.6.58

No fixed version is known at submission time.

Confirmed source sweep:

v3.0.0   ToolsMCPServer.run_sse helper present, no Origin/Host/auth checks
v3.10.0  praisonai mcp run --transport sse wraps configured tools into helper
v3.12.3  praisonai serve mcp --name --transport sse wraps configured tools
v4.0.0   same vulnerable helper and CLI wrapping paths
v4.4.12  same vulnerable helper and CLI wrapping paths
v4.5.0   same vulnerable helper and CLI wrapping paths
v4.5.56  same vulnerable helper and CLI wrapping paths
v4.5.139 same vulnerable helper and CLI wrapping paths
v4.6.57  same vulnerable helper and CLI wrapping paths
v4.6.58  same vulnerable helper and dynamic PoV succeeds

Advisory History

Visible PraisonAI advisories were checked before this report was prepared.

Nearby advisories are distinct:

  • GHSA-wj6g-v78p-6fx3: Origin validation bypass in the MCP HTTP Stream transport. This report targets the legacy SSE ToolsMCPServer.run_sse() path, which has no Origin/Host/auth guard at all.
  • GHSA-pvph-5j39-v8qc: prefix-match origin validation bypass in the PraisonAI MCP HTTP server. This report is not a bypass of a weak validation function; the SSE wrapper never invokes validation.
  • GHSA-wv94-5qcp-6m36: unbounded session accumulation in MCP HTTP server. This report is a cross-origin/host authorization boundary issue.
  • GHSA-9cr9-25q5-8prj: arbitrary file read in MCP CLI tools. This report is transport-level unauthorized access to whichever registered tools are exposed.
  • prior reports: none cover ToolsMCPServer.run_sse() or the legacy SSE Host/Origin/Auth guard gap.

References

https://github.com/MervinPraison/PraisonAI/security/policy

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H

CVE ID

CVE-2026-57112

Weaknesses

Missing Authentication for Critical Function

The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources. Learn more on MITRE.

Origin Validation Error

The product does not properly verify that the source of data or communication is valid. Learn more on MITRE.

Missing Authorization

The product does not perform an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

Credits