# Constant Contact Forms <= 2.22.0 - Improper Authentication to Unauthenticated Mailing List Subscription of Arbitrary Users via Login Opt-in

- **ID:** WPSEC-2026-0670
- **Plugin:** Constant Contact Forms (`constant-contact-forms`), https://wordpress.org/plugins/constant-contact-forms/
- **Affected versions:** all versions before 2.22.1
- **Fixed in:** 2.22.1 (Update to 2.22.1 or later.)
- **Severity:** Medium 5.3 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)
- **Weakness:** CWE-287
- **Usage among sites WPSec scans:** plugin Medium, affected versions Medium (as of 2026-10-08)
- **Attack surface analysis:** https://attacksurface.wpsec.com/plugin/constant-contact-forms
- **Fix released:** 2026-10-07
- **Published:** 2026-10-08
- **URL:** https://wpsec.com/vuln/WPSEC-2026-0670/

## Description

The Constant Contact Forms plugin for WordPress is vulnerable to Improper Authentication in all versions up to, and including, 2.22.0. The login opt-in handler ran before WordPress verified the submitted password, did not check whether the login opt-in was enabled, and identified the account by the submitted username alone. This makes it possible for unauthenticated attackers who know a username to subscribe that user's email address to the site's Constant Contact mailing lists without the user's consent.

## References

- https://wpsec.com/vuln/WPSEC-2026-0670/
- https://plugins.svn.wordpress.org/constant-contact-forms/tags/2.22.1/
- https://wordpress.org/plugins/constant-contact-forms/

Source: WPSec, https://wpsec.com/vuln/WPSEC-2026-0670/

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.