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CVE-2026-85661 — excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when…

Key facts

CVE-2026-85661 is a Critical (9.8) vulnerability: excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when…. This entry ships a detection-only PoC and a Docker test lab.
CVE CVE-2026-85661
Severity Critical (9.8)
Detection / prevention —
PoC poc.py
Source 2026/CVE-2026-85661/

Details

English | 한국어

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.

Vulnerability Details

Property Value
CVE ID CVE-2026-85661
Type RCE
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-85661/poc.py

Usage

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start

# Clone and navigate to CVE directory
cd CVE-2026-85661

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints

Application URL Status
Vulnerable App http://localhost:8080 Shows vulnerability
Patched App http://localhost:8081 Demonstrates fix

Directory Structure

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

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

Generated by PoC Generator on 2026-09-05T01:33:12.917860695

Frequently asked questions

What is CVE-2026-85661?

CVE-2026-85661 is a Critical (9.8) vulnerability: excel-mcp-server 0.1.8 fails to enforce path confinement in stdio mode when…. This entry ships a detection-only PoC and a Docker test lab.

How do I detect CVE-2026-85661?

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2026-85661?

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

For authorized security testing and research only. See the full source and NVD record.