Contact Form 7 Signature Addon <= 4.2.2 - Unauthenticated Arbitrary File Read via Path Traversal in Email Attachments

The Contact Form 7 Signature Addon WordPress plugin through 4.2.2 does not sanitize a signature field value before building an email attachment path from it, allowing unauthenticated users to attach arbitrary files (bounded to wp-content on current Contact Form 7) to a form's outgoing email via path traversal; when a form is configured to email a copy to a submitter-controlled address, the attacker can read the targeted file.