CVE-2026-94589 in Extensions for CF7 Plugin
Summary
by MITRE • 10/10/2026
The Extensions For CF7 (Contact form 7 Database, Conditional Fields and Redirection) plugin for WordPress is vulnerable to Arbitrary File Upload in all versions up to, and including, 3.4.5 via the extcf7_submit function. This is due to missing file extension, MIME type, and size validation in the signature field's validation_filter(), combined with the absence of PHP-execution guards in the upload directory and a sanitize_file_name() bypass that converts shell.php- into shell.php. This makes it possible for unauthenticated attackers to upload files that may be executable, which makes remote code execution possible.
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Analysis
by VulDB Data Team • 10/10/2026
The Extensions For CF7 plugin, specifically versions up through 3.4.5, contains a critical security flaw within its extcf7_submit function that allows unauthenticated users to perform arbitrary file uploads on the targeted WordPress installation. This vulnerability stems from insufficient input validation and sanitization mechanisms during the processing of form submissions. The core issue lies in the signature field's validation_filter(), which fails to enforce strict checks on file extensions, MIME types, or maximum file sizes before accepting uploaded content for storage. By neglecting these fundamental security controls, the application inadvertently trusts user-supplied data without verifying its integrity or safety, creating a direct pathway for malicious actors to inject executable scripts into the server environment.
The technical execution of this exploit relies on a specific bypass technique involving the sanitize_file_name() function. Attackers can manipulate file names by appending characters that are stripped during sanitization but preserved in subsequent processing steps. For instance, an attacker might attempt to upload a file named shell.php-; while the system attempts to sanitize the name, it may strip the trailing hyphen or other non-alphanumeric characters depending on configuration, resulting in the final stored filename being recognized as shell.php by the web server. This bypass effectively neutralizes any basic extension filtering that relies solely on string matching without accounting for such edge cases. Furthermore, the upload directory lacks PHP-execution guards, meaning there are no additional safeguards like .htaccess rules or specific server configurations to prevent scripts from executing even if they manage to bypass initial validation checks.
The operational impact of this vulnerability is severe, as it directly leads to remote code execution on the affected system. Once an attacker successfully uploads a malicious PHP script via the vulnerable form submission endpoint, they can access and execute that script through standard HTTP requests. This grants the attacker full control over the web server's context, allowing them to read sensitive data, modify website content, install backdoors, or pivot further into the internal network infrastructure. Since this vulnerability exists in all versions up to 3.4.5 and requires no authentication, it is easily exploitable by automated scanning tools and opportunistic attackers targeting WordPress sites that have not yet applied updates or implemented compensating controls.
From a classification perspective, this flaw aligns with CWE-434, which describes the unrestricted upload of files with dangerous types, as well as CWE-20, indicating improper input validation where external data is accepted without sufficient verification. In terms of attack behavior mapping to MITRE ATT&CK techniques, this vulnerability facilitates T1505.003, Server Side Web Shell, and potentially T1190, Exploit Public-Facing Application, as it allows an attacker to leverage a publicly accessible interface to gain initial access and establish persistence through uploaded malicious scripts.
To mitigate this risk, administrators should immediately update the Extensions For CF7 plugin to version 3.4.6 or later, where these validation issues have been addressed. If updating is not immediately feasible, implementing compensating controls such as disabling PHP execution in the WordPress uploads directory via server configuration files like .htaccess for Apache or equivalent directives for Nginx can significantly reduce the impact of successful file uploads. Additionally, deploying a Web Application Firewall that monitors form submissions for anomalous patterns and restricts upload capabilities to authenticated users only can provide an additional layer of defense against exploitation attempts until the software is fully patched.