Post SMTP <= 4.0.1 - Unauthenticated Stored DOM-Based Cross-Site Scripting via 'user_email' Parameter (Multisite Registration → Failed Email Log)
Strategic Overview
- Status
- Patched in 4.0.2
- Affected Plugin
- Post SMTP – Complete Email Delivery and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App
- Affected Version
<= 4.0.1- CVSS
- 7.2High
- Weakness type
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
- CVE
CVE-2026-75962
At a glance
CVE-2026-75962 is a high-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Post SMTP WordPress plugin, affecting versions <= 4.0.1. It carries a CVSS score of 7.2 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 4.0.2; sites on affected versions should update now. Disclosed October 2026, reported by Adrien Brunner.
Vulnerability Overview
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 'user_email' 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.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no privileges on the target site, and no interaction from a victim user.
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Post SMTP <= 4.0.1 carries this weakness at user_email, and reaching it takes no account at all. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.
Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For Post SMTP the fix is 4.0.2: builds <= 4.0.1 are affected, anything from 4.0.2 onward is not.
Remediation
Update to version 4.0.2, or a newer patched version
How does WordSec protect against this?
Requests carrying this pattern arrive without a session, so nothing upstream of the firewall gets a chance to reject them: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Post SMTP 4.0.2 closes this, and updating the plugin is the step that ends it.
- Firewall
- Login Security
- Alerts
External References
Related records
Same weakness class
Other vulnerabilities in Post SMTP – Complete Email Delivery and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App
- 9.8CVE-2025-11833: Post SMTP Account Takeover
CVE-2025-11833 - 9.8CVE-2023-6875: POST SMTP Mailer Authorization Bypass
CVE-2023-6875 - 8.8CVE-2025-24000: Post SMTP Authenticated (Subscriber+) Account Takeover
CVE-2025-24000 - 7.2CVE-2024-5207: POST SMTP Mailer SQL Injection
CVE-2024-5207 - 7.2CVE-2023-6620: POST SMTP Mailer SQL Injection
CVE-2023-6620 - 7.2CVE-2023-5958: POST SMTP Mailer <= 2.7.0 Stored Cross-Site Scripting
CVE-2023-5958 - 7.2Post SMTP <= 2.6.0 SQL Injection
- 7.2CVE-2023-3082: Post SMTP <= 2.5.7 Stored Cross-Site Scripting
CVE-2023-3082
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