CVE-2026-7400: filesystem-mcp-server Path Traversal Flaw

CVE-2026-7400 Overview

A path traversal vulnerability has been identified in geekgod382 filesystem-mcp-server version 1.0.0. This security flaw affects the is_path_allowed function within the server.py file, specifically impacting the read_file_tool and write_file_tool components. The vulnerability allows remote attackers to bypass intended path restrictions and access or modify files outside of the designated allowed directories through path traversal sequences.

Critical Impact
Remote attackers can exploit this path traversal vulnerability to read sensitive files or write malicious content to arbitrary locations on the server filesystem, potentially leading to information disclosure, data corruption, or further system compromise.

Affected Products

geekgod382 filesystem-mcp-server version 1.0.0
Systems utilizing the vulnerable read_file_tool and write_file_tool components
MCP server deployments with network-accessible file operations

Discovery Timeline

April 29, 2026 - CVE-2026-7400 published to NVD
April 29, 2026 - Last updated in NVD database

Technical Details for CVE-2026-7400

Vulnerability Analysis

This path traversal vulnerability (CWE-22) exists in the filesystem-mcp-server's path validation mechanism. The is_path_allowed function in server.py fails to properly sanitize and validate user-supplied file paths before processing file read and write operations. This inadequate validation allows attackers to use path traversal sequences (such as ../) to escape the intended directory boundaries.

The vulnerability is remotely exploitable without requiring authentication or user interaction. When exploited, an attacker can traverse the directory structure to access files outside the configured ALLOWED_PATHS, potentially reading configuration files, credentials, or other sensitive data. The write capability presents additional risk as attackers could potentially modify system files or plant malicious content.

Root Cause

The root cause of this vulnerability lies in the improper implementation of the is_path_allowed function, which fails to adequately enforce ALLOWED_PATHS restrictions. The path validation logic can be bypassed through crafted input containing directory traversal sequences. The function does not properly resolve and canonicalize paths before comparing them against the allowed path list, enabling attackers to supply paths that appear valid but ultimately resolve to unauthorized locations.

Attack Vector

The attack is network-based and can be executed remotely against any exposed filesystem-mcp-server instance running version 1.0.0. An attacker crafts a malicious request to either the read_file_tool or write_file_tool endpoint, embedding path traversal sequences within the file path parameter. The server processes the request without proper validation, allowing the attacker to:

Read arbitrary files by requesting paths like ../../etc/passwd through the read_file_tool
Write arbitrary content to sensitive locations using similar techniques with write_file_tool

The exploit has been publicly disclosed, increasing the risk of widespread exploitation.

The security patch involved changes to project configuration and path validation logic. The relevant commit (45364545fc60dc80aadcd4379f08042d3d3d292e) addressed the ALLOWED_PATHS check bypass issue.

Source: GitHub Commit Details

Detection Methods for CVE-2026-7400

Indicators of Compromise

Unusual file access patterns in server logs showing path traversal sequences (../, ..\, etc.)
Access attempts to sensitive system files like /etc/passwd, /etc/shadow, or configuration files
Write operations to directories outside of configured ALLOWED_PATHS
HTTP requests to read_file_tool or write_file_tool endpoints containing encoded traversal characters (%2e%2e%2f)

Detection Strategies

Implement web application firewall (WAF) rules to detect and block path traversal patterns in request parameters
Deploy file integrity monitoring (FIM) on sensitive directories to detect unauthorized read or write activity
Configure intrusion detection systems (IDS) with signatures for common path traversal attack patterns
Review server.py access logs for requests containing suspicious path patterns targeting file operation endpoints

Monitoring Recommendations

Enable detailed logging for the filesystem-mcp-server application, specifically for file access operations
Monitor network traffic for anomalous requests to the MCP server file handling endpoints
Set up alerts for access attempts to files outside the designated ALLOWED_PATHS directories
Implement real-time log analysis to correlate path traversal attempts with potential data exfiltration

How to Mitigate CVE-2026-7400

Immediate Actions Required

Upgrade to filesystem-mcp-server version 1.1.0 or later immediately
Review server logs for evidence of exploitation attempts
Audit files that may have been accessed or modified through the vulnerable endpoints
Temporarily disable network access to vulnerable server instances if immediate patching is not possible

Patch Information

The vulnerability has been addressed in filesystem-mcp-server version 1.1.0. The security patch is identified by commit hash 45364545fc60dc80aadcd4379f08042d3d3d292e. Organizations should upgrade to the patched version as soon as possible.

Relevant resources:

Workarounds

Restrict network access to the filesystem-mcp-server to trusted IP addresses only using firewall rules
Implement an additional reverse proxy layer with path validation to filter malicious requests
Configure strict ALLOWED_PATHS settings and ensure the underlying filesystem permissions limit access
Consider running the service in a containerized environment with minimal filesystem exposure

bash

# Example: Restrict network access to filesystem-mcp-server using iptables
# Allow only trusted internal network (adjust IP range as needed)
iptables -A INPUT -p tcp --dport 8080 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP