CVE-2026-85661: excel-mcp-server 0.1.8 Arbitrary File Read/Write via stdio mode
excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when EXCELFILESPATH is unset, allowing attackers to read and write arbitrary files. Attackers can supply unchecked file paths to read and write tools to access any file accessible to the process.
Affected Software
Event History
Frequently Asked Questions
Under what configuration is the server affected?
The issue occurs in stdio mode when EXCEL_FILES_PATH is unset. In that condition, file paths supplied to the read and write tools are not confined to an intended directory.
What does an attacker need to exploit this issue?
An attacker needs the ability to supply file paths to the server's read or write tools. No privileges or user interaction are required according to the supplied severity vector.
What files can be accessed or modified?
An attacker can read or write any file that is accessible to the excel-mcp-server process. The effective impact therefore depends on the operating-system permissions and credentials under which that process runs.