The vulnerability is a path traversal flaw (CWE‑22) that permits an unauthenticated attacker to supply crafted file paths to any of the 25 exposed MCP tool handlers. In SSE or Streamable‑HTTP transport mode the server is intended to confine file operations to the directory set by the EXCEL_FILES_PATH environment variable, but the enforcement function fails to check absolute paths and does not resolve relative paths, allowing the attacker to read, write, or overwrite any file on the host filesystem. This could lead to unauthorized data disclosure, tampering, or potentially execution of malicious code if files are written where they can be executed.

The affected product is haris‑musa's excel‑mcp‑server, with versions up to and including 0.1.7 vulnerable. The vulnerability is relevant when the server runs in SSE or Streamable‑HTTP transport mode, which are the documented methods for remote use. The server relies on the EXCEL_FILES_PATH environment variable to limit file operations, but this checkpoint is bypassed by the flaw.

The CVSS score is 9.4, indicating high severity, and the EPSS score is not available; it is not listed in the CISA KEV catalog. The default configuration binds to 0.0.0.0 (all interfaces) with no authentication, giving an attacker trivial remote access to the vulnerability. Attack conditions require only network connectivity to the exposed transport, making exploitation straightforward.