# MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot, AWeber Etc. <= 1.2.78.4 - Unauthenticated Admin Email Flooding via subscribe_to_email_list

- **ID:** WPSEC-2026-0461
- **Plugin:** MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot, AWeber Etc. (`mailoptin`), https://wordpress.org/plugins/mailoptin/
- **Affected versions:** all versions before 1.2.78.5
- **Fixed in:** 1.2.78.5 (Update to 1.2.78.5 or later.)
- **Severity:** Medium 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L)
- **Weakness:** CWE-770
- **Usage among sites WPSec scans:** plugin Medium, affected versions Medium (as of 2026-10-06)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/mailoptin
- **Fix released:** 2026-10-05
- **Published:** 2026-10-06
- **URL:** https://wpsec.com/vuln/WPSEC-2026-0461/

## Description

The MailOptin plugin for WordPress is vulnerable to admin email flooding in all versions up to, and including, 1.2.78.4. The public subscribe_to_email_list action does not check that the submitted opt-in campaign exists and has no rate limiting, and the plugin emails the site administrator an error notification, without any throttling, each time a subscription fails because no email provider or list is set for the campaign. This makes it possible for unauthenticated attackers to send repeated subscription requests naming a non-existent campaign, each of which sends an error email to the site administrator and stores a junk lead record.

## References

- https://wpsec.com/vuln/WPSEC-2026-0461/
- https://plugins.svn.wordpress.org/mailoptin/tags/1.2.78.5/
- https://wordpress.org/plugins/mailoptin/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-0461/

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.