CVE-2026-55156 Token Optimizer MCP: Unauthenticated Path Traversal in Dashboard Session Log API Endpoints
Unauthenticated attackers can read arbitrary JSONL files via path traversal in the dashboard API, exposing sensitive session data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55156?
CVE-2026-55156 is a medium-severity path traversal vulnerability in ooples token-optimizer-mcp, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-22
Which versions are affected by CVE-2026-55156?
2 open source packages ship an affected version, including @ooples/token-optimizer-mcp.
| Package | Affected | Fixed in |
|---|---|---|
@ooples/token-optimizer-mcp npm | All versions | 5.1.0 |
@ooples/token-optimizer-mcp npm | All versions | 5.1.0 |
How do I fix CVE-2026-55156?
Upgrade @ooples/token-optimizer-mcp to 5.1.0 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-55156 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55156 exists.
Sources
Also known as GHSA-76pc-mqxp-3rq5.