# MailPoet – Newsletters, Email Marketing, and Automation <= 5.41.0 - Unauthenticated Open Redirect via 'referrer_form_url' Parameter

- **ID:** WPSEC-2026-0949
- **Plugin:** MailPoet – Newsletters, Email Marketing, and Automation (`mailpoet`), https://wordpress.org/plugins/mailpoet/
- **Affected versions:** all versions before 5.42.0
- **Fixed in:** 5.42.0 (Update to 5.42.0 or later.)
- **Severity:** Medium 6.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)
- **Weakness:** CWE-601
- **Usage among sites WPSec scans:** plugin Medium, affected versions Medium (as of 2026-10-14)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/mailpoet
- **Fix released:** 2026-10-13
- **Published:** 2026-10-14
- **URL:** https://wpsec.com/vuln/WPSEC-2026-0949/

## Description

The MailPoet plugin for WordPress is vulnerable to Open Redirect via the 'referrer_form_url' parameter of the CAPTCHA page shown for WordPress and WooCommerce registration forms in all versions up to, and including, 5.41.0, due to the CAPTCHA page using the request-supplied 'referrer_form_url' value as the form's submission target without validating its host, and rendering every other request value as a hidden form field. This makes it possible for unauthenticated attackers to craft a link to the site's CAPTCHA page whose form sends the visitor, and the data the form submits, to an attacker-controlled external site when the visitor submits the CAPTCHA.

## References

- https://wpsec.com/vuln/WPSEC-2026-0949/
- https://plugins.svn.wordpress.org/mailpoet/tags/5.42.0/
- https://wordpress.org/plugins/mailpoet/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-0949/

License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Free to use, share and adapt, also commercially, if you credit WPSec and link to this advisory.