CVE-2026-33989: Mobile MCP Path Traversal Vulnerability

CVE-2026-33989 Overview

CVE-2026-33989 is a Path Traversal vulnerability discovered in Mobile Next, an MCP (Model Context Protocol) server designed for mobile development and automation. The vulnerability exists in the @mobilenext/mobile-mcp server package, specifically affecting the mobile_save_screenshot and mobile_start_screen_recording tools. The saveTo and output parameters were passed directly to filesystem operations without proper validation, enabling attackers to write files to arbitrary locations outside the intended workspace directory.

Critical Impact

Attackers can exploit this path traversal vulnerability to write malicious files outside the designated workspace, potentially overwriting critical system files, injecting malicious content, or achieving further compromise of the affected system.

Affected Products

• Mobile Next MCP Server (@mobilenext/mobile-mcp) versions prior to 0.0.49
• Node.js deployments running vulnerable Mobile MCP packages
• Mobile development and automation environments utilizing Mobile Next MCP

Discovery Timeline

• 2026-03-27 - CVE-2026-33989 published to NVD
• 2026-03-31 - Last updated in NVD database

Technical Details for CVE-2026-33989

Vulnerability Analysis

This vulnerability is classified as CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), commonly known as Path Traversal. The core issue stems from insufficient input validation in the Mobile Next MCP server's file handling operations. When users invoke the mobile_save_screenshot or mobile_start_screen_recording tools, the server accepts user-supplied paths through the saveTo and output parameters respectively. These parameters are then used directly in filesystem write operations without sanitization or boundary checking.

The vulnerability allows an attacker with network access to manipulate the file path parameters by injecting directory traversal sequences (such as ../) to escape the intended workspace directory. This can lead to arbitrary file writes on the underlying system, which presents significant security implications including the ability to overwrite configuration files, plant malicious scripts, or corrupt application data.

Root Cause

The root cause is the direct use of user-supplied input in filesystem operations without implementing path canonicalization or validation against a permitted directory structure. The affected functions failed to:

1. Normalize the provided path to resolve traversal sequences
2. Verify the resolved path remains within the designated workspace boundaries
3. Reject paths containing dangerous traversal patterns

This represents a classic path traversal vulnerability pattern where trust is implicitly placed in user-supplied file paths without proper security controls.

Attack Vector

An attacker can exploit this vulnerability remotely over the network. The attack requires some user interaction, such as triggering a screenshot save or screen recording operation with a malicious path parameter. The attacker crafts a request containing traversal sequences in the saveTo or output parameters.

For example, instead of providing a legitimate path like ./screenshots/capture.png, an attacker could supply a path such as ../../etc/cron.d/malicious to write files outside the workspace. The MCP server processes this path without validation, resulting in file creation at the attacker-specified location.

The vulnerability enables arbitrary file writes but does not directly expose confidential data (no impact to confidentiality). However, the integrity impact is significant as attackers can modify or create files anywhere the server process has write permissions.

Detection Methods for CVE-2026-33989

Indicators of Compromise

• Unexpected file creations in system directories outside the Mobile MCP workspace
• Log entries showing file operations with path traversal sequences (../, ..\, or URL-encoded variants)
• New or modified files in sensitive directories such as /etc/, /var/, or application configuration paths
• Anomalous MCP server activity involving mobile_save_screenshot or mobile_start_screen_recording calls

Detection Strategies

• Implement file integrity monitoring (FIM) on critical system directories to detect unauthorized file writes
• Monitor Mobile MCP server logs for requests containing path traversal patterns in saveTo or output parameters
• Deploy web application firewall (WAF) rules to detect and block requests with directory traversal sequences
• Use endpoint detection and response (EDR) solutions to track file system operations originating from the MCP server process

Monitoring Recommendations

• Enable verbose logging for the Mobile MCP server to capture all file operation requests
• Set up alerts for file creation events outside the expected workspace directory hierarchy
• Monitor process behavior for the Node.js process running Mobile MCP for suspicious filesystem access patterns
• Review audit logs for any attempts to access sensitive system paths from the MCP server context

How to Mitigate CVE-2026-33989

Immediate Actions Required

• Upgrade @mobilenext/mobile-mcp to version 0.0.49 or later immediately
• Audit existing deployments for signs of exploitation by checking for unexpected files outside workspace directories
• Review and restrict filesystem permissions for the user account running the MCP server
• Implement network segmentation to limit exposure of Mobile MCP server instances

Patch Information

The vulnerability has been addressed in Mobile Next MCP Server version 0.0.49. The fix implements proper path validation to ensure file operations remain within the intended workspace boundaries. Organizations should upgrade to this version or later to remediate the vulnerability.

For detailed information about the fix, refer to the GitHub Security Advisory GHSA-3p2m-h2v6-g9mx and the security patch commit.

Workarounds

• If immediate patching is not possible, consider restricting network access to the Mobile MCP server to trusted sources only
• Run the MCP server in a containerized or sandboxed environment with minimal filesystem permissions
• Implement a reverse proxy or application-layer firewall that filters requests containing path traversal patterns
• Temporarily disable the mobile_save_screenshot and mobile_start_screen_recording features until the patch can be applied

# Upgrade Mobile MCP to the patched version
npm update @mobilenext/mobile-mcp@0.0.49

# Verify the installed version
npm list @mobilenext/mobile-mcp