A security vulnerability has been discovered in the Jannis Thuemmig Email Encoder plugin (versions <= 2.1.8) which inappropriately neutralizes input during web page generation, leading to Cross-site Scripting (XSS) attacks. Here, we dive into the details of this vulnerability, its implications, and the remediation steps that should be taken. This article is intended for those who have a basic understanding of HTML, JavaScript, and web applications.

(For a refresher, check out these resources: HTML, JavaScript, Web Applications)

Vulnerability Details (CVE-2023-47821)

The vulnerability in question is related to "Improper Neutralization of Input During Web Page Generation "Cross-site Scripting" (CWE-79)". It has been assigned the CVE ID CVE-2023-47821.

Email Encoder plugin (versions <= 2.1.8) fails to sufficiently sanitize user input when encoding email addresses, resulting in an XSS vulnerability. An attacker can exploit this by injecting malicious JavaScript code into a web page that uses the vulnerable Email Encoder plugin, ultimately leading to unauthorized access to sensitive data or control over the affected system.

Below is a sample code snippet that demonstrates the vulnerability

<a href="mailto:test@example.com?subject={{XSS_Payload}}">
    Contact us

Where {{XSS_Payload}} is replaced with a malicious JavaScript payload by the attacker.

Exploit Details

To exploit this vulnerability, an attacker needs to craft a specially formatted email address containing malicious JavaScript code, which, when encoded by the vulnerable plugin, would result in an XSS attack.

For example, an attacker may use a payload such as this


When input into the Email Encoder plugin, this malicious code is not properly sanitized and could result in the execution of the attacker's script in the affected user's browser, leading to full control of the user's session or unauthorized access to sensitive data.

Original References

1. CVE-2023-47821 - National Vulnerability Database (NVD)
2. CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') - Common Weakness Enumeration (CWE)
3. Jannis Thuemmig Email Encoder plugin - Official Repository

To address this vulnerability and protect your system, please follow these steps

1. Update the Email Encoder plugin to the latest version (2.1.9 or later), which has patched the vulnerability. This can be done via the plugin manager or by downloading and installing it from the official repository.

2. Ensure that all user input is properly sanitized throughout your application. This includes not only input from forms (e.g., contact forms, search forms) but also input passed from URLs and included in HTML attributes.

3. Regularly review and update your security policies and practices, including updating plugins, themes, and other software used on your site.


CVE-2023-47821 represents a significant security risk for any web application utilizing the Email Encoder plugin versions <= 2.1.8. Ensuring that you have up-to-date software and security practices is crucial in protecting your application and user-base from potential exploitation.


Published on: 11/22/2023 23:15:00 UTC
Last modified on: 11/28/2023 20:23:00 UTC