CVE-2026-85661: excel-mcp-server 0.1.8 Arbitrary File Read/Write via stdio mode

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-04 · updated 2026-09-23
Weakness: CWE-22

Description

excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when EXCEL_FILES_PATH 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 products

haris-musa excel-mcp-server: through 0.1.8

References

https://github.com/haris-musa/excel-mcp-server
https://github.com/haris-musa/excel-mcp-server/blob/v0.1.8/src/excel_mcp/server.py
https://github.com/haris-musa/excel-mcp-server/blob/v0.1.8/src/excel_mcp/validation.py
https://github.com/haris-musa/excel-mcp-server/issues/149
https://www.vulncheck.com/advisories/excel-mcp-server-0.1.8-arbitrary-file-read-write-via-stdio-mode

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