CVE-2026-75962: Post SMTP <= 4.0.1 - Unauthenticated Stored DOM-Based Cross-Site Scripting via 'user_email' Parameter (Multisite Registration → Failed Email Log)
The Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'useremail' parameter in all versions up to, and including, 4.0.1 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. This is exploitable without authentication on WordPress Multisite installations with public registration enabled, as WordPress accepts email addresses containing numeric HTML character references that Post SMTP's stricter validator rejects, persisting the attacker-controlled address verbatim to the email log via the failed-send exception message.
Affected Software
Event History
Frequently Asked Questions
Which WordPress sites are exposed to unauthenticated exploitation?
The described unauthenticated path applies to WordPress Multisite installations with public registration enabled. An attacker can submit a crafted user_email value during registration, causing it to be stored in a failed email log.
What attacker access or interaction is required?
No authentication or user interaction is required to inject the payload. The stored script executes when a user accesses the injected page containing the affected email-log content.
Are default single-site WordPress installations affected by the described exploit path?
The provided exploit path specifically requires WordPress Multisite with public registration enabled. The data does not establish unauthenticated exploitation for single-site installations or Multisite sites without public registration.
Which plugin versions are affected?
All Post SMTP versions up to and including 4.0.1 are affected according to the provided data.