CVE-2026-55156
Received Received - Intake

Unauthenticated Path Traversal in Token Optimizer MCP

Publication date: 2026-09-28

Last updated on: 2026-09-28

Assigner: GitHub, Inc.

Description
Token Optimizer MCP measures token savings per AI coding agent, optimizes context, and shares a live local knowledge graph across 16 CLI clients. Prior to version 5.1.0, 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. This issue has been patched in version 5.1.0.

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Meta Information

Published
2026-09-28
Last Modified
2026-09-28
Generated
2026-09-28
AI Q&A
2026-09-28
EPSS Evaluated
N/A
NVD
CVE-2026-55156
EUVD
EUVD-2026-88398

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
ooples token_optimizer_mcp to 5.1.0 (exc)
ooples token_optimizer_mcp 5.1.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-22 The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

Attack-Flow Graph

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Executive Summary

CVE-2026-55156 is a path traversal vulnerability in the token-optimizer-mcp package affecting versions up to 5.0.1. The dashboard HTTP server exposes unauthenticated API endpoints /api/session-summary and /api/session-events that concatenate an unsanitized sessionId query parameter directly into a filesystem path. This allows Node.js to normalize path traversal sequences like ../, enabling unauthenticated attackers to read any .jsonl file accessible to the server, including sensitive session logs.

Detection Guidance

Check if your token-optimizer-mcp instance is running version 5.0.1 or earlier. Inspect network traffic for unauthenticated requests to /api/session-summary or /api/session-events endpoints with sessionId parameters containing path traversal sequences like ../. Verify if sensitive .jsonl files are accessible without authentication.

Impact Analysis

An unauthenticated attacker could exploit this to read sensitive files on the server, including session logs containing tool invocations, hook outputs, and token usage data. This could lead to exposure of proprietary AI agent interactions, internal tool configurations, or other confidential information stored in accessible .jsonl files.

Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, potentially violating GDPR (data protection) and HIPAA (health information privacy) by exposing personal or protected health information stored in session logs or other accessible files. Compliance may be impacted if such data exposure occurs.

Mitigation Strategies

Upgrade to version 5.1.0 or later immediately. Add authentication middleware to /api/* routes. Validate sessionId using path.basename or a strict allowlist to prevent path traversal. Restrict network access to the dashboard HTTP server if possible.

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