Image CAPTCHA Bypass in Contact Form 7 and WPForms

Executive Summary

This vulnerability is a CAPTCHA bypass in the Image CAPTCHA for Contact Form 7 and WPForms plugin versions up to 3.3.29. It allows unauthenticated attackers to bypass the CAPTCHA protection by submitting a hardcoded static answer, specifically 'kc_captcha=kc_human', which passes validation without solving the CAPTCHA. This enables automated spam submissions and abuse of forms relying solely on this CAPTCHA.

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Detection Guidance

Check if the Image CAPTCHA for Contact Form 7 and WPForms plugin version 3.3.29 or earlier is installed. Inspect HTTP requests to forms using this plugin for the presence of the static parameter kc_captcha=kc_human, which indicates exploitation.

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Impact Analysis

This vulnerability enables attackers to automate spam submissions and abuse forms protected by the plugin. It undermines the intended anti-automation control, allowing bots to bypass CAPTCHA validation and submit spam or abuse form actions that depend on CAPTCHA protection.

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Compliance Impact

The plugin was marketed as GDPR-compliant due to its use of inline SVGs without external requests or storage, but the bypass vulnerability weakens its intended privacy and security controls. Compliance with GDPR or HIPAA may be impacted if the vulnerability leads to unauthorized data collection or spam-related breaches, as it undermines the plugin's spam protection claims.

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Mitigation Strategies

Disable the Image CAPTCHA for Contact Form 7 and WPForms plugin immediately. Replace it with an alternative CAPTCHA solution or enable additional anti-spam measures like honeypot fields or rate limiting on forms.

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