CVE-2026-56058: Quform Path Traversal Vulnerability

CVE-2026-56058 Overview

CVE-2026-56058 is an arbitrary file upload vulnerability in the Quform WordPress plugin affecting versions up to and including 2.23.0. The flaw allows an authenticated user with Subscriber-level privileges to upload arbitrary files to the WordPress server. Because the plugin fails to properly validate uploaded file types, attackers can place executable content such as PHP scripts into web-accessible paths. This weakness is classified under CWE-434: Unrestricted Upload of File with Dangerous Type. The issue was published to the National Vulnerability Database (NVD) on 2026-06-26.

Critical Impact
A low-privileged Subscriber account can upload arbitrary files, achieve remote code execution on the WordPress host, and pivot to full site compromise.

Affected Products

Quform WordPress plugin versions <= 2.23.0
WordPress sites permitting Subscriber registration with Quform installed
Any web host running vulnerable Quform releases with public form endpoints

Discovery Timeline

2026-06-26 - CVE-2026-56058 published to NVD
2026-06-26 - Last updated in NVD database

Technical Details for CVE-2026-56058

Vulnerability Analysis

The Quform plugin exposes form-processing endpoints that accept file uploads as part of form submissions. In versions <= 2.23.0, the upload handler does not enforce sufficient validation on file extensions, MIME types, or content structure. A Subscriber-authenticated request can therefore submit files with executable extensions such as .php or double extensions that bypass naive filtering. The uploaded artifact is written to a location reachable by the web server, converting a form submission into arbitrary code execution.

Exploitation requires only Subscriber-level credentials, which many WordPress deployments grant through open self-registration. The attacker interacts across the network, needs no user interaction, and the impact crosses trust boundaries into the underlying operating system context of the PHP worker.

Root Cause

The root cause is missing or bypassable server-side validation of uploaded file content and extension in the Quform submission handler. The plugin relies on client-controllable metadata rather than authoritative server-side checks against a strict allow-list of file types. This is a textbook manifestation of CWE-434.

Attack Vector

An attacker registers or authenticates as a Subscriber, then submits a crafted multipart form request to a Quform-backed form endpoint. The request includes a malicious file whose extension or MIME type is not blocked by the plugin. Once written to disk in a web-accessible directory, the attacker requests the uploaded file directly, causing the web server to execute its contents. See the Patchstack WordPress Vulnerability Report for advisory details.

No verified public exploit code is referenced in the advisory data. The vulnerability mechanism is described in prose in place of synthetic proof-of-concept code.

Detection Methods for CVE-2026-56058

Indicators of Compromise

New files with executable extensions such as .php, .phtml, or .phar inside wp-content/uploads/quform/ or related plugin upload directories.
Unexpected HTTP POST requests to Quform submission endpoints originating from newly created Subscriber accounts.
Outbound network connections initiated by the PHP worker to unfamiliar hosts shortly after form submissions.

Detection Strategies

Monitor WordPress wp-content/uploads/ recursively for files whose extensions or magic bytes indicate server-executable content.
Correlate Subscriber account creation events with subsequent POST traffic to Quform endpoints and file writes on disk.
Deploy web application firewall (WAF) rules that inspect multipart uploads for disallowed extensions and PHP tags in file bodies.

Monitoring Recommendations

Enable file integrity monitoring across the WordPress document root and alert on new executable file creation.
Log and review all authenticated form submissions, capturing user ID, filename, MIME type, and destination path.
Track process lineage where the web server user (www-data, nginx, or equivalent) spawns shells or network utilities.

How to Mitigate CVE-2026-56058

Immediate Actions Required

Update the Quform plugin to a version later than 2.23.0 once the vendor publishes a fix.
Audit existing Subscriber accounts and disable open user registration if not required.
Inspect wp-content/uploads/ for unauthorized executable files and remove any confirmed web shells.

Patch Information

Refer to the Patchstack WordPress Vulnerability Report for the authoritative patch and fixed-version information. Apply the vendor-supplied update through the WordPress admin console or by replacing the plugin files directly.

Workarounds

Temporarily deactivate the Quform plugin until a patched version is installed.
Restrict Subscriber-role access to form endpoints via a WAF or access control plugin.
Configure the web server to deny execution of PHP within the plugin's upload directory using directives such as php_flag engine off or an equivalent Nginx location block.

bash

# Configuration example: deny PHP execution in Quform upload path (Apache)
<Directory "/var/www/html/wp-content/uploads/quform">
    <FilesMatch "\.(php|phtml|phar|php[0-9]+)$">
        Require all denied
    </FilesMatch>
    php_flag engine off
</Directory>