Webheadcoder Multi-Step Forms for Contact Form 7 <= 4.7 - Reflected Cross-Site Scripting via 'l10n_print_after' Parameter

The Webheadcoder Multi-Step Forms for Contact Form 7 plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'l10n_print_after' parameter in all versions up to, and including, 4.7 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link. Successful exploitation requires that the targeted site has at least one Contact Form 7 form configured with a [multistep] form-tag, as the canonicalization introduced in version 4.7 blocks the attack path on non-multistep forms.