PYSEC-2026-3426

Description

Impact

wireshark-mcp exposes a wireshark_export_objects MCP tool that accepts an attacker-controlled dest_dir parameter and passes it to tshark's --export-objects flag with no mandatory path restriction.

The path sandbox (_allowed_dirs) is None by default and only activates when the environment variable WIRESHARK_MCP_ALLOWED_DIRS is explicitly set. In a default installation, any directory on the filesystem can be used as the export destination.

Affected code (src/wireshark_mcp/tshark/client.py:531-543):

output_validation = self._validate_output_path(dest_dir)

# _validate_output_path only enforces the sandbox when _allowed_dirs is set.

# Default: _allowed_dirs = None → no restriction.

os.makedirs(dest_dir, exist_ok=True)   # creates arbitrary directories

cmd = [..., "--export-objects", f"{protocol},{dest_dir}"]

Attack Scenario

An attacker embeds a crafted HTTP response in a pcap file (e.g. Content-Disposition: filename=authorized_keys). Via prompt injection in the pcap payload, an AI model using this MCP server is manipulated into calling wireshark_export_objects with:

dest_dir=/home/user/.ssh/

tshark then extracts and writes the HTTP object to that path, granting the attacker SSH access.

The same technique can target:

• /etc/cron.d/

• Writable web roots

• Other sensitive filesystem locations

Additional Affected Operations

The same missing sandbox affects:

• merge_pcap_files

• editcap_trim

• editcap_split

• editcap_time_shift

• editcap_deduplicate

• text2pcap_import

Proof of Concept

Confirmed on wireshark-mcp v1.1.5 with tshark 4.6.4.

A crafted pcap’s HTTP object was successfully written to an arbitrary filesystem path when:

_allowed_dirs = None

Patches

Not yet patched.

A fix should make the path sandbox mandatory for all file-write operations rather than optional:

# Reject all write operations when no sandbox is configured

if not self._allowed_dirs:

    return json.dumps({

        "success": False,

        "error": {

            "type": "SecurityError",

            "message": "Set WIRESHARK_MCP_ALLOWED_DIRS before using file-write operations"

        }

    })

Workarounds

Set WIRESHARK_MCP_ALLOWED_DIRS to a restricted safe directory before starting the server:

export WIRESHARK_MCP_ALLOWED_DIRS=/tmp/wireshark_mcp_safe

This activates the existing sandbox and blocks writes outside the allowed path.

Resources

• Vulnerable code:

  • src/wireshark_mcp/tshark/client.py lines 521–543

  • src/wireshark_mcp/tshark/client.py lines 685–839

• CWE-22: Improper Limitation of a Pathname to a Restricted Directory

• CWE-73: External Control of File Name or Path