Drag and Drop File Upload for Contact Form 7 <= 1.1.3 - Unauthenticated Arbitrary File Upload via sanitize_file_name Bypass

The Drag and Drop File Upload for Contact Form 7 plugin for WordPress is vulnerable to arbitrary file upload in versions up to, and including, 1.1.3. This is due to the plugin extracting the file extension before sanitization occurs and allowing the file type parameter to be controlled by the attacker rather than being restricted to administrator-configured values, which when combined with the fact that validation occurs on the unsanitized extension while the file is saved with a sanitized extension, allows special characters like '$' to be stripped during the save process. This makes it possible for unauthenticated attackers to upload arbitrary PHP files and potentially achieve remote code execution, however, an .htaccess file and name randomization is in place which restricts real-world exploitability.

Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Drag and Drop File Upload for Contact Form 7 1.1.4 closes this, and updating the plugin is the step that ends it.

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