CVE-2026-44556: Open webui Open WebUI's Responses Passthrough Endpoint Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hp5m-24vp-vq2q",
  "modified" : "2026-05-15T23:52:36Z",
  "published" : "2026-05-08T19:45:53Z",
  "aliases" : [ "CVE-2026-44556" ],
  "summary" : "Open WebUI's responses passthrough endpoint lacks access control authorization",
  "details" : "## Summary\n\nThe /responses endpoint in the OpenAI router accepts any authenticated user and forwards requests directly to upstream LLM providers without enforcing per-model access control. While the primary chat completion endpoint (generate_chat_completion) checks model ownership, group membership, and AccessGrants before allowing a request, the /responses proxy only validates that the user has a valid session via get_verified_user.\n\nThis allows any authenticated user — regardless of role or group assignment — to interact with any model configured on the instance by sending a POST request to /api/openai/responses with an arbitrary model ID.\n\n## Impact\n\nAs per OWASP TOP 10 LLM:\n\n- **Model Denial of Service (OWASP LLM04):** An unauthorized user can submit resource-intensive requests to expensive models (e.g., o1-pro, GPT-4o) that were explicitly restricted by the administrator. In shared deployments, this can exhaust API budgets or rate limits, causing total service disruption for all legitimate users.\n\n- **Model Theft (OWASP LLM10):** If the instance proxies access to fine-tuned or self-hosted models, unauthorized users can freely interact with them, enabling capability extraction or model distillation without authorization.\n\n- **Access Policy Bypass:** Administrators lose the ability to enforce cost-tier restrictions, team-based model assignments, or compliance boundaries through the existing access control system.\n\nThe endpoint is a raw passthrough proxy and does not resolve workspace model configurations (system prompts, knowledge bases, RAG pipelines). Therefore, workspace-specific confidential data is not directly exposed through this vector.\n\nPR: https://github.com/open-webui/open-webui/pull/23481",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "open-webui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.9.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.8.12"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/security/advisories/GHSA-hp5m-24vp-vq2q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44556"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/open-webui/open-webui/pull/23481"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/open-webui/open-webui"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-284", "CWE-862" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-08T19:45:53Z",
    "nvd_published_at" : "2026-05-15T20:16:47Z"
  }
}