---
id: CVE-2026-109515
title: >-
  MailOptin <= 1.2.78.6 - Unauthenticated Privilege Escalation to
  'form_custom_field_mappings' Parameter
summary: >-
  The MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot,
  AWeber Etc. plugin for WordPress is vulnerable to Privilege Escalation in all
  versions up to, and including, 1.2.78.6 This is due to the
  `subscribe_to_email_l…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-269
vendor: properfraction
product: >-
  MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot,
  AWeber Etc.
affected:
  - >-
    mailoptin_popup_optin_forms_email_newsletters_for_mailchimp_hubspot_aweber_etc.
    <= 1.2.78.6
published: '2026-10-16'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T04:27:01.480Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-109515'
references:
  - url: >-
      https://www.wordfence.com/threat-intel/vulnerabilities/id/96111116-6b6f-42fc-98d8-6f5c27dc3c1c?source=cve
  - url: >-
      https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/connections/WordPressUserRegistrationConnect/Subscription.php#L68
  - url: >-
      https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/core/src/Connections/AbstractConnect.php#L84
  - url: >-
      https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/core/src/AjaxHandler.php#L699
  - url: >-
      https://plugins.trac.wordpress.org/changeset?reponame=&new=3744644%40mailoptin%2Ftrunk&old=3738326%40mailoptin%2Ftrunk#file4
  - url: >-
      https://plugins.trac.wordpress.org/changeset/3744644/mailoptin/trunk/src/connections/WordPressUserRegistrationConnect/Subscription.php
tags:
  - cve.org
ingestedAt: '2026-10-16T04:58:47.491Z'
---

## Overview

The MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot, AWeber Etc. plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 1.2.78.6 This is due to the `subscribe_to_email_list` endpoint accepting an attacker-supplied `optin_data[form_custom_field_mappings]` parameter without any allow-list validation on destination keys, allowing the attacker-controlled mapping to override the administrator's saved mapping and pass arbitrary `wp_users` column names — including `ID` and `user_pass` — directly into `wp_insert_user()` via the `subscribe()` function. This makes it possible for unauthenticated attackers to force `wp_insert_user()` into UPDATE mode on any existing account by supplying a target user's numeric `ID`, overwrite that account's password with a pre-hashed value of their choosing, and thereby take over any WordPress user account — including administrators — leading to full site compromise. Exploitation requires that a WordPress User Registration opt-in form is published somewhere on the site, though the form's UUID is visible in page source and no authentication, nonce, or capability check is required to reach the vulnerable endpoint.

## Affected

- `mailoptin_popup_optin_forms_email_newsletters_for_mailchimp_hubspot_aweber_etc. <= 1.2.78.6`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.