CVE-2026-18781 Overview
CVE-2026-18781 affects the Drag and Drop Multiple File Upload for Contact Form 7 WordPress plugin in versions prior to 1.3.9.9. The plugin fails to validate the final filename of an uploaded file after stripping characters from it. This flaw allows unauthenticated attackers to bypass file type restrictions and upload files that execute as server-side code. The vulnerability maps to [CWE-94] Improper Control of Generation of Code, indicating a code injection weakness reachable over the network without authentication.
Critical Impact
Unauthenticated remote attackers can upload arbitrary files and achieve remote code execution on vulnerable WordPress sites.
Affected Products
- Drag and Drop Multiple File Upload for Contact Form 7 WordPress plugin versions before 1.3.9.9
- WordPress installations with the affected plugin activated
- Sites using Contact Form 7 with the vulnerable file upload extension
Discovery Timeline
- 2026-08-21 - CVE-2026-18781 published to NVD
- 2026-08-26 - Last updated in NVD database
Technical Details for CVE-2026-18781
Vulnerability Analysis
The Drag and Drop Multiple File Upload plugin extends Contact Form 7 with a drag-and-drop file upload widget. To prevent malicious uploads, the plugin defines a denylist of disallowed extensions and strips unwanted characters from submitted filenames. The vulnerability arises because the plugin evaluates the filename before sanitization rather than after. Character-stripping transforms a name that appears safe into one with an executable extension, defeating the restriction entirely.
An attacker submits a filename crafted so that removed characters expose an executable extension such as .php. The plugin accepts the file under its pre-strip name, then stores it under the post-strip name on disk. Requesting the file through the web server triggers PHP execution in the context of the WordPress process.
Because the upload endpoint is exposed to unauthenticated users through the contact form, no credentials or user interaction beyond a crafted HTTP request are required. Successful exploitation grants attackers a foothold with the privileges of the web server, enabling webshell deployment, database access, and lateral movement into the WordPress environment.
Root Cause
The root cause is order-of-operations in filename validation. The plugin validates the extension against its denylist before applying character stripping. The stripped filename is never revalidated, so any transformation that produces a forbidden extension slips past the check.
Attack Vector
Exploitation occurs over the network against any page that renders a Contact Form 7 form using the plugin's drag-and-drop upload field. The attacker crafts a multipart form submission containing a file whose original name includes obfuscation characters that the plugin removes. After stripping, the file is written to the plugin's upload directory with an executable extension. See the WPScan Vulnerability Report for further technical details.
Detection Methods for CVE-2026-18781
Indicators of Compromise
- Files with executable extensions such as .php, .phtml, or .phar present in the plugin's upload directory, typically under wp-content/uploads/wp_dndcf7_uploads/
- Filenames containing unusual character sequences, whitespace, or double extensions that suggest denylist evasion attempts
- Outbound connections or new administrative user accounts created shortly after suspicious multipart POST requests to Contact Form 7 endpoints
Detection Strategies
- Inspect web server access logs for POST requests to wp-admin/admin-ajax.php with the dnd_codedropz_upload action followed by GET requests to files in the upload directory
- Alert on any request that serves a .php or other executable file from within the wp-content/uploads/ tree
- Compare filenames recorded by the plugin against files actually written to disk to identify sanitization-induced discrepancies
Monitoring Recommendations
- Enable WordPress file integrity monitoring on wp-content/uploads/ and alert on the creation of any file with a scripting extension
- Forward web server, PHP-FPM, and WordPress audit logs to a centralized SIEM for correlation of upload events with subsequent execution
- Track plugin version inventory across WordPress deployments and flag any instance running a build earlier than 1.3.9.9
How to Mitigate CVE-2026-18781
Immediate Actions Required
- Update the Drag and Drop Multiple File Upload for Contact Form 7 plugin to version 1.3.9.9 or later on every affected WordPress site
- Audit the plugin's upload directory for unexpected files with executable extensions and remove any that are found
- Rotate WordPress administrator credentials and API keys if evidence of exploitation exists
Patch Information
The vendor addressed the flaw in version 1.3.9.9 of the plugin by validating the final filename after character stripping. Site operators should install the update through the WordPress plugin manager or replace the plugin files manually. Refer to the WPScan Vulnerability Report for advisory details.
Workarounds
- Deactivate the Drag and Drop Multiple File Upload plugin until the patched version can be deployed
- Block execution of PHP and other scripting handlers within wp-content/uploads/ using web server configuration such as an .htaccess rule or Nginx location directive
- Deploy a web application firewall rule that denies multipart uploads containing filenames with control characters or double extensions to Contact Form 7 endpoints
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
