Path Traversal Vulnerability in mail-mcp-bridge

A path traversal vulnerability, identified as CVE-2026-7386, has been discovered in fatbobman mail-mcp-bridge version 1.3.3 and prior. The vulnerability resides within the src/mail_mcp_server.py file, specifically affecting an unspecified function that handles the message_ids argument. A remote attacker can exploit this flaw by crafting malicious requests containing manipulated message_ids values. Successful exploitation allows the attacker to traverse the file system and potentially read sensitive files. An exploit is publicly available. The vulnerability is addressed in version 1.3.4, with patch 638b162b26532e32fa8d8047f638537dbdfe197a.

Attack Chain

1. The attacker identifies a vulnerable instance of mail-mcp-bridge running version 1.3.3 or earlier.
2. The attacker crafts a malicious HTTP request targeting the endpoint that processes message_ids.
3. Within the request, the attacker includes a message_ids parameter containing path traversal sequences (e.g., ../).
4. The server-side application, without proper validation, processes the manipulated message_ids value.
5. The application attempts to access a file path constructed using the attacker-controlled input.
6. Due to the path traversal sequences, the application accesses a file outside the intended directory.
7. The application reads the contents of the traversed file.
8. The attacker retrieves the contents of the file, gaining access to sensitive information.

Impact

Successful exploitation of this vulnerability allows an attacker to read arbitrary files on the server. This could lead to the exposure of sensitive data such as configuration files, application source code, or user data. With a CVSS v3.1 base score of 7.3, this vulnerability poses a significant risk. The number of affected installations is unknown, but any instance of mail-mcp-bridge running a vulnerable version is susceptible to attack.

Recommendation

• Upgrade fatbobman mail-mcp-bridge to version 1.3.4 or later to apply the patch 638b162b26532e32fa8d8047f638537dbdfe197a that resolves CVE-2026-7386.
• Deploy the Sigma rule “Detect mail-mcp-bridge Path Traversal Attempt” to identify exploitation attempts in web server logs.
• Implement input validation on the message_ids parameter to prevent path traversal attacks in web applications, even after patching.