MailOptin Plugin up to 1.2.78.6 on WordPress subscribe_to_email_list endpoint wp_insert_user optin_data[form_custom_field_mappings] privileges management

Summaryinfo

A vulnerability categorized as critical has been discovered in MailOptin Plugin up to 1.2.78.6. This impacts the function wp_insert_user of the component subscribe_to_email_list endpoint. Such manipulation of the argument optin_data[form_custom_field_mappings] leads to privileges management. This vulnerability is referenced as CVE-2026-109515. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in MailOptin Plugin up to 1.2.78.6. It has been rated as critical. Affected by this issue is the function wp_insert_user of the component subscribe_to_email_list endpoint. The manipulation of the argument optin_data[form_custom_field_mappings] with an unknown input leads to a privileges management vulnerability. Using CWE to declare the problem leads to CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at wordfence.com. This vulnerability is handled as CVE-2026-109515 since 10/12/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 10/16/2026). The MITRE ATT&CK project declares the attack technique as T1068.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• WordPress Plugin

Name

• MailOptin Plugin

Version

• 1.2.78.0
• 1.2.78.1
• 1.2.78.2
• 1.2.78.3
• 1.2.78.4
• 1.2.78.5
• 1.2.78.6

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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