Compliance Impact

The vulnerability allows arbitrary file read and write operations, which can lead to exposure or modification of sensitive local files. This poses high confidentiality and integrity risks.

Such risks can impact compliance with standards and regulations like GDPR and HIPAA, which require protection of sensitive data and prevention of unauthorized access or modification.

Specifically, unauthorized file access or alteration could lead to breaches of personal or health information, violating data protection requirements.

Mitigations such as restricting file operations to a configured workspace, disabling write capabilities for untrusted users, and running the server under low-privilege accounts are recommended to reduce compliance risks.

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Executive Summary

The vulnerability CVE-2026-10278 involves an arbitrary file read and write issue in the excel-mcp tool. It arises because multiple MCP tools accept file path arguments such as filePath, sourceFile, outputPath, and outputFile without enforcing restrictions like a workspace root, sandbox directory, or allowlist.

This lack of validation allows attackers who can invoke these tools to perform path traversal attacks, enabling them to read supported spreadsheet files or write CSV/XLS/XLSX files to arbitrary paths writable by the server process.

The root cause is that the MCP tool arguments are passed directly to filesystem read/write APIs without proper validation, which can be exploited remotely.

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Impact Analysis

This vulnerability can have significant impacts on confidentiality and integrity. Attackers can read local files that should be protected or overwrite files by writing new CSV or spreadsheet files outside the intended repository directory.

Such unauthorized file access and modification can expose sensitive data or corrupt important files, leading to data breaches or operational issues.

The availability impact is considered low, but the confidentiality and integrity risks are high.

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Detection Guidance

This vulnerability can be detected by checking if the excel-mcp tool is invoked with file path arguments such as filePath, sourceFile, outputPath, or outputFile that are not properly validated or restricted. Specifically, look for usage that allows reading or writing files outside of a designated workspace or sandbox directory.

Detection can involve monitoring for suspicious commands or API calls that attempt to read or write spreadsheet or CSV files to arbitrary paths writable by the server process.

• Inspect logs or command invocations for arguments passed to read_file or write_file functions that include absolute paths or paths traversing outside the expected directory.
• Use static analysis or manual code review to identify if the MCP tool arguments are passed directly to filesystem APIs without validation.

Example commands to detect potential exploitation attempts might include searching for usage patterns like:

• grep -rE "read_file|write_file" /path/to/excel-mcp/logs
• grep -rE "filePath=|outputPath=|sourceFile=|outputFile=" /path/to/excel-mcp/logs
• Monitoring network traffic for remote calls invoking these tools with suspicious path arguments.

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Mitigation Strategies

Immediate mitigation steps include restricting file operations to a configured workspace directory to prevent path traversal outside allowed areas.

Disable or restrict write-capable tools for untrusted callers to reduce the risk of arbitrary file writes.

Run the MCP server under a low-privilege account to limit the impact of any successful exploitation.

Implement validation to enforce path containment, reject absolute paths unless explicitly allowed, and add regression tests to prevent recurrence.

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