CVE-2026-7386: mail-mcp-bridge Path Traversal Flaw

CVE-2026-7386 Overview

A path traversal vulnerability has been discovered in fatbobman mail-mcp-bridge versions up to 1.3.3. The flaw exists in the file src/mail_mcp_server.py where manipulation of the message_ids argument allows attackers to traverse directory paths. This vulnerability can be exploited remotely, and a public exploit has been disclosed. The vulnerability has been patched in version 1.3.4.

Critical Impact
Remote attackers can exploit this path traversal vulnerability to access files outside of intended directories by manipulating the message_ids parameter, potentially exposing sensitive email attachments and system files.

Affected Products

fatbobman mail-mcp-bridge versions up to 1.3.3
macOS Mail email access service components using vulnerable mail-mcp-bridge

Discovery Timeline

2026-04-29 - CVE-2026-7386 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7386

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Path Traversal), a common weakness where user-controlled input is used to construct file paths without proper validation. In the case of mail-mcp-bridge, the message_ids parameter is processed without adequate sanitization, allowing attackers to inject path traversal sequences such as ../ to escape the intended directory structure.

The mail-mcp-bridge component serves as a bridge for accessing macOS Mail email data, including email content reading, thread retrieval, and attachment extraction. When the application processes message IDs for attachment handling, it fails to validate that the resulting path remains within the expected directory boundaries, enabling unauthorized file access.

Root Cause

The root cause lies in insufficient input validation of Message-ID values before they are used to construct filesystem paths. Message-IDs are untrusted external input that can contain malicious path components. Without proper normalization and validation, these values can be crafted to traverse outside the intended attachment directory structure.

Attack Vector

The attack vector is network-based, meaning exploitation can occur remotely without requiring local access to the target system. An attacker can send specially crafted requests containing malicious message_ids values with path traversal sequences to access arbitrary files on the server's filesystem. The attack complexity is low, requiring no authentication or special privileges.

The following code shows the security patch that was applied to fix the vulnerability:

python

#!/usr/bin/env python3
"""
Helpers for safely mapping message IDs onto attachment directories.
"""

import base64
from pathlib import Path
from typing import Union


def normalize_message_id(message_id: str) -> str:
    """
    Normalize a Message-ID for use as a directory name.

    Message-ID values are untrusted input. We only allow a single path segment
    after stripping optional angle brackets.
    """
    clean_message_id = message_id.strip().strip('<>')

    if not clean_message_id:
        raise ValueError("Message-ID is empty")

    return clean_message_id


def get_message_dir_name(message_id: str) -> str:
    """
    Encode a Message-ID into a single safe directory name.
    """
    clean_message_id = normalize_message_id(message_id)

Source: GitHub Commit

Detection Methods for CVE-2026-7386

Indicators of Compromise

Unusual file access patterns in mail-mcp-bridge logs showing path traversal sequences such as ../, ..%2f, or ..%5c in message_ids parameters
Access attempts to files outside the designated attachment directories
Error logs indicating failed attempts to access restricted filesystem paths
Unexpected file reads or directory listings from the mail-mcp-bridge service

Detection Strategies

Monitor application logs for message_ids parameters containing path traversal indicators including encoded variants
Implement file integrity monitoring on sensitive directories that should not be accessed by the mail service
Deploy web application firewall (WAF) rules to detect and block path traversal patterns in incoming requests
Review access logs for anomalous file access patterns outside normal attachment directories

Monitoring Recommendations

Enable detailed logging for the mail-mcp-bridge service to capture all message_ids parameter values
Configure alerts for any file access attempts outside the expected attachment storage paths
Implement runtime application self-protection (RASP) to detect path traversal attempts in real-time
Regularly audit filesystem access patterns from the mail-mcp-bridge process

How to Mitigate CVE-2026-7386

Immediate Actions Required

Upgrade mail-mcp-bridge to version 1.3.4 or later immediately
Review access logs to identify any potential exploitation attempts prior to patching
Audit any files that may have been accessed through this vulnerability
If upgrade is not immediately possible, restrict network access to the mail-mcp-bridge service

Patch Information

The vulnerability has been addressed in mail-mcp-bridge version 1.3.4. The fix introduces a new src/attachment_paths.py module that properly normalizes and validates Message-ID values before using them to construct filesystem paths. The security patch is identified by commit 638b162b26532e32fa8d8047f638537dbdfe197a.

Upgrade instructions and release notes are available at the GitHub Release Notes. Additional details about the vulnerability can be found in the GitHub Issue Tracker.

Workarounds

Restrict network access to the mail-mcp-bridge service to trusted IP addresses only until patching is complete
Implement additional input validation at the network perimeter using a WAF or reverse proxy
Run the mail-mcp-bridge service with minimal filesystem permissions to limit the impact of exploitation
Consider containerizing the service with restricted filesystem mount points

bash

# Configuration example - Restrict service access via firewall
# Only allow access from trusted internal networks
iptables -A INPUT -p tcp --dport 8080 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP

# Verify installed version
pip show mail-mcp-bridge | grep Version

# Upgrade to patched version
pip install --upgrade mail-mcp-bridge>=1.3.4