CVE-2026-55157: Token Optimizer MCP

The National Vulnerability Database (NVD) record says that before version 5.1.0, token-optimizer-mcp is vulnerable to operating system command injection in the smart_user tool, letting any Model Context Protocol (MCP) client that can call it execute arbitrary shell commands; fixed in 5.1.0.

The record

Kind

Vulnerability

Source record

CVE-2026-55157: Token Optimizer MCP measures token savings per AI coding agent, optimizes context, and shares a live local kno (National Vulnerability Database record)

Record published

2026-09-28

Posted here

2026-10-12

World

Software agents · Enterprise work agents

Controls concerned

Containment and isolation C-E5

Checked

Checked against its record on 2026-10-22 by a reader who did not draft it; report verification/reports/SIG-2026-10-12-004-2026-10-22.md.

A signal's controls are the ones its record points at, the exposure; a case's controls are the ones its records show were absent or failed, so the two can differ.

Corrections

Changes to what this signal says, with the reason. Every earlier version is kept.

• 2026-10-22: Summary. Found in an independent read against the record on 22 October 2026: the record's claim was stated in the Register's own voice and omitted the effect and the fix (CVE record CVE-2026-55157).
  Show the change

  Before: Prior to version 5.1.0, token-optimizer-mcp is vulnerable to OS command injection in the smart_user tool.

  After: The National Vulnerability Database (NVD) record says that before version 5.1.0, token-optimizer-mcp is vulnerable to operating system command injection in the smart_user tool, letting any Model Context Protocol (MCP) client that can call it execute arbitrary shell commands; fixed in 5.1.0.

What a signal is. A signal records what a primary record says; it assigns no fault. It is lighter than a case: one dated item from one record, tagged with the world, sector and controls it touches. It becomes a case when it meets the bar for one.

Newer: CVE-2026-55096: fast-mcp-telegram
Older: UK AI Security Institute incident report: agents in a cyber evaluation