Executive brief
excel-mcp-server is a tool that integrates Excel file manipulation into AI assistant workflows via the Model Context Protocol. When the EXCEL_FILES_PATH environment variable is not configured, the server fails to restrict file access, allowing attackers to read and write any file accessible to the process, potentially exposing sensitive data or modifying critical system files.
Technical details
The vulnerability is a path traversal / broken access control issue in excel-mcp-server version 0.1.8 that occurs in stdio mode when the EXCEL_FILES_PATH environment variable is unset. The read and write tools accept file paths without validation against a confinement boundary, permitting attackers to supply absolute or relative paths that traverse outside the intended directory. The attack requires network access to the MCP server instance or direct command injection via an AI assistant endpoint. An attacker can achieve arbitrary file read and write on the host system with the privileges of the process. The issue has been reported and tracked under CVE-2026-85661.
Affected products
- haris-musa excel-mcp-server 0.1.8
Timeline
- 2026-09-04: disclosed: CVE-2026-85661 published on NVD