GHSA-94F4-HR76-P5J6

Vulnerability from github – Published: 2026-06-16 17:36 – Updated: 2026-06-16 17:36
VLAI
Summary
vLLM: OpenAI auth bypass
Details

Summary

A vulnerability in ASGI web servers and starlette's trust on those web servers enables an authentication bypass of the OpenAI API AuthenticationMiddleware, which was discovered during @x41sec's source code audit. It allows to use the API without providing the configured VLLM_API_KEY or --api-key.

Details

In https://github.com/vllm-project/vllm/blob/v0.14.0/vllm/entrypoints/openai/api_server.py#L689-L692 the url_path is taken from the URL, which is reconstructed by starlette based on the request scope.

from starlette.datastructures import URL, Headers, MutableHeaders, State

# ...

url_path = URL(scope=scope).path.removeprefix(root_path)
headers = Headers(scope=scope)
if url_path.startswith("/v1") and not self.verify_token(headers):
    response = JSONResponse(content={"error": "Unauthorized"}, status_code=401)
    return response(scope, receive, send)
return self.app(scope, receive, send)

The request scope includes the request's Host: header and reconstructs the URL as shown below:

f"{scheme}://{host_header}{path}"

Neither starlette nor any of the ASGI servers (including uvicorn, which vllm uses) properly filter the Host: header for invalid characters. This allows an attacker to include special URL characters such as / or ? in the Host: header and thereby control the reconstructed URL and it's .path attribute.

FastAPI/starlette's routing uses the HTTP path and does not depend on the parsed url.path attribute, allowing attackers to reach an endpoint via a certain path while providing a different value in the .path.

Impact

  • Instances of vllm that use an API Key for the OpenAI API and expose the API to attackers.
  • Instances behind an RFC-conforming web server (such as nginx) are not affected.
Severity
9.1 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "vllm"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.3.0"
            },
            {
              "fixed": "0.22.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48746"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-444"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-16T17:36:41Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Summary\n\nA vulnerability in ASGI web servers and starlette\u0027s trust on those web servers enables an authentication bypass of the OpenAI API `AuthenticationMiddleware`, which was discovered during @x41sec\u0027s source code audit.\nIt allows to use the API without providing the configured `VLLM_API_KEY` or `--api-key`.\n\n### Details\n\nIn https://github.com/vllm-project/vllm/blob/v0.14.0/vllm/entrypoints/openai/api_server.py#L689-L692 the `url_path` is taken from the `URL`, which is reconstructed by _starlette_ based on the request `scope`.\n\n```py\nfrom starlette.datastructures import URL, Headers, MutableHeaders, State\n\n# ...\n\nurl_path = URL(scope=scope).path.removeprefix(root_path)\nheaders = Headers(scope=scope)\nif url_path.startswith(\"/v1\") and not self.verify_token(headers):\n    response = JSONResponse(content={\"error\": \"Unauthorized\"}, status_code=401)\n    return response(scope, receive, send)\nreturn self.app(scope, receive, send)\n```\n\nThe request `scope` includes the request\u0027s `Host:` header and reconstructs the URL as shown below:\n\n```py\nf\"{scheme}://{host_header}{path}\"\n```\n\nNeither starlette nor [any of the ASGI servers](https://asgi.readthedocs.io/en/latest/implementations.html#servers) (including uvicorn, which vllm uses) properly filter the `Host:` header for invalid characters. This allows an attacker to include special URL characters such as `/` or `?` in the `Host:` header and thereby control the reconstructed URL and it\u0027s `.path` attribute.\n\nFastAPI/starlette\u0027s routing uses the HTTP path and does not depend on the parsed url.path attribute, allowing attackers to reach an endpoint via a certain path while providing a different value in the `.path`.\n\n### Impact\n- Instances of vllm that use an API Key for the OpenAI API and expose the API to attackers.\n- Instances behind an RFC-conforming web server (such as nginx) are **not** affected.",
  "id": "GHSA-94f4-hr76-p5j6",
  "modified": "2026-06-16T17:36:41Z",
  "published": "2026-06-16T17:36:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/security/advisories/GHSA-94f4-hr76-p5j6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vllm-project/vllm/pull/43426"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/vllm-project/vllm"
    },
    {
      "type": "WEB",
      "url": "https://x41-dsec.de/lab/advisories/x41-2026-002-starlette"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "vLLM: OpenAI auth bypass"
}



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