CVE-2026-85661

excel-mcp-server 0.1.8 (CWE-22, path traversal) fails to enforce path confinement when running in stdio mode with the EXCEL_FILES_PATH environment variable unset, so its read and write tools accept arbitrary file paths without validation. An attacker, typically an untrusted prompt or agent interacting with the MCP server, can supply unchecked paths to read or overwrite any file accessible to the process. Impact is rated high across confidentiality, integrity, and availability, with a CVSS 4.0 score of 9.3 (critical). Only deployments of excel-mcp-server 0.1.8 in stdio mode without EXCEL_FILES_PATH configured are affected. There is no public proof-of-concept, no CISA KEV listing, and a low EPSS probability of 0.4% over 30 days, indicating no known exploitation at this time.

What to do: Upgrade excel-mcp-server to a release newer than 0.1.8 once a patched version is published, and in the meantime always set EXCEL_FILES_PATH to a dedicated, restricted directory when launching the server in stdio mode. Run the process under an OS account whose file access is limited to intended spreadsheet directories, and review which AI clients or agents are permitted to invoke its read and write tools.