CVE-2026-1306: midi-Synth WordPress Plugin RCE Vulnerability

CVE-2026-1306 Overview

The midi-Synth plugin for WordPress contains a critical arbitrary file upload vulnerability due to missing file type and file extension validation in the export AJAX action. This vulnerability affects all versions up to and including 1.1.0, allowing unauthenticated attackers to upload arbitrary files to the affected site's server, potentially leading to remote code execution.

The severity of this vulnerability is compounded by the fact that the required nonce for exploitation is exposed in frontend JavaScript, making it trivially accessible to unauthenticated attackers without any special access or privileges.

Critical Impact

Unauthenticated attackers can upload arbitrary files including PHP webshells to achieve remote code execution on vulnerable WordPress installations. The nonce required for exploitation is exposed in frontend JavaScript, eliminating the primary authentication barrier.

Affected Products

• midi-Synth WordPress Plugin versions up to and including 1.1.0
• WordPress installations with the vulnerable midi-Synth plugin active

Discovery Timeline

• February 14, 2026 - CVE-2026-1306 published to NVD
• February 18, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1306

Vulnerability Analysis

This vulnerability is classified as CWE-434 (Unrestricted Upload of File with Dangerous Type), one of the most severe file upload vulnerabilities. The midi-Synth plugin fails to implement proper file type validation and file extension checks in its export AJAX action handler, creating a direct path for attackers to upload malicious files.

The attack requires no authentication because the AJAX nonce—intended as a security mechanism to prevent unauthorized requests—is inadvertently exposed in the frontend JavaScript code. This design flaw means any visitor to a page where the plugin is loaded can extract the valid nonce and use it to make authorized AJAX requests to the vulnerable endpoint.

Once an attacker successfully uploads a malicious file (such as a PHP webshell), they can execute arbitrary code with the privileges of the web server user, potentially leading to full server compromise.

Root Cause

The root cause of this vulnerability is the absence of proper input validation in the file upload handler within the export AJAX action. Specifically, the plugin fails to:

1. Validate the MIME type of uploaded files
2. Check and restrict file extensions to safe types
3. Properly secure the nonce from frontend exposure

The vulnerable code can be found in midiSynth.php around lines 110-121 and in midiSynthConvert.php around lines 421-492, where file upload processing occurs without adequate security controls.

Attack Vector

The attack can be executed remotely over the network by any unauthenticated user. The attacker first obtains the valid nonce from the frontend JavaScript code served by the plugin. With this nonce, they craft a malicious AJAX request to the export action endpoint, including an arbitrary file payload such as a PHP webshell.

Upon successful upload, the malicious file is stored on the server in a web-accessible location. The attacker can then request this file directly to execute arbitrary PHP code, achieving remote code execution with the privileges of the web server process.

Detection Methods for CVE-2026-1306

Indicators of Compromise

• Unexpected PHP files appearing in WordPress upload directories or plugin folders
• Web server logs showing POST requests to /wp-admin/admin-ajax.php with action=export from suspicious IP addresses
• Evidence of webshell files (e.g., files containing functions like eval(), base64_decode(), system(), or exec())
• Anomalous outbound network connections from the web server process

Detection Strategies

• Monitor WordPress AJAX endpoints for unusual file upload activity targeting the export action
• Implement file integrity monitoring to detect new or modified PHP files in the WordPress installation
• Deploy web application firewalls (WAF) with rules to block suspicious file upload attempts
• Review server access logs for patterns of exploitation attempts against admin-ajax.php

Monitoring Recommendations

• Enable detailed logging for WordPress AJAX requests and file system changes
• Configure alerting for new executable files created in web-accessible directories
• Implement SentinelOne Singularity platform for real-time endpoint detection and response
• Regularly audit installed WordPress plugins for known vulnerabilities using security scanning tools

How to Mitigate CVE-2026-1306

Immediate Actions Required

• Deactivate and remove the midi-Synth plugin immediately if running version 1.1.0 or earlier
• Audit the WordPress installation for any suspicious files that may have been uploaded
• Review server logs for evidence of exploitation attempts
• Consider temporarily restricting access to admin-ajax.php if the plugin cannot be immediately removed

Patch Information

As of the last NVD update on February 18, 2026, no official patch has been confirmed. Website administrators should monitor the Wordfence Vulnerability Report and the official WordPress plugin repository for updates. Until a patched version is released, complete removal of the plugin is recommended.

Additional technical details about the vulnerable code can be found in the WordPress Plugin Source Code.

Workarounds

• Remove or deactivate the midi-Synth plugin entirely until a patched version is available
• Implement web application firewall rules to block requests to the vulnerable export AJAX action
• Restrict access to admin-ajax.php to authenticated users only if feasible for your site configuration
• Use file upload monitoring tools to detect and quarantine suspicious uploads in real-time

# Disable the vulnerable plugin via WP-CLI
wp plugin deactivate midi-synth

# Search for recently uploaded PHP files that may indicate compromise
find /var/www/html/wp-content -name "*.php" -mtime -7 -type f

# Check for common webshell indicators in uploaded files
grep -r "eval\|base64_decode\|system\|passthru\|shell_exec" /var/www/html/wp-content/uploads/