During testing of the Ultimate Posts Widget plugin for WordPress, a security vulnerability was identified that allows for Stored Cross-Site Scripting (XSS) attacks. The vulnerability arises from the plugin’s failure to properly validate and escape certain widget options before outputting them back in attributes. As a result, high privilege users such as administrators can exploit this flaw to execute malicious scripts, potentially leading to account takeover (if an attacker has previously hijacked an administrator or editor account, he can plant a backdoor to regain access back).

Main info:

PluginUltimate Posts Widget < 2.3.1
All Time461 602
Active installations10 000+
Publicly PublishedFebruary 20, 2023
Last UpdatedFebruary 20, 2023
ResearcherDmtirii Ignatyev
OWASP TOP-10A7: Cross-Site Scripting (XSS)
Reference https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-0561
Plugin Security Certification by CleanTalk


January 12, 2023Plugin testing and vulnerability detection in the Ultimate Posts Widget have been completed
January 12, 2023I contacted the author of the plugin and provided a vulnerability PoC with a description and recommendations for fixing
February 5, 2023The author fixed the vulnerability and released the plugin update
February 20, 2023Registered CVE-2024-0561

Discovery of the Vulnerability

In the process of testing the plugin, a vulnerability was found that allows you to implement Stored XSS on behalf of the editor by embedding the widget in a main page, which entails account takeover

Understanding of Stored XSS attack’s

Stored XSS vulnerabilities occur when user-supplied input is not properly sanitized before being stored and displayed back to other users. In WordPress, this can occur when plugins or themes fail to sanitize input fields or widget options, allowing attackers to inject malicious scripts that are executed within the context of other users’ browsers. Real examples of Stored XSS in WordPress include injecting scripts into comment sections, form fields, or widget content, which can then be executed when other users view the affected pages.

Exploiting the Stored XSS Vulnerability


  1. When creating a new widget, insert the following payload in the “CSS” field – ” onmouseover=”alert(/XSS/)”


To exploit the Stored XSS vulnerability in the Ultimate Posts Widget plugin, an attacker with administrator-level privileges can create a new widget and insert a malicious payload in the “CSS” field. The payload could include JavaScript code designed to perform malicious actions, such as stealing session cookies, redirecting users to phishing sites, or performing other unauthorized activities. When other users, including administrators, view the affected page or post containing the widget, the injected scripts are executed within their browsers, allowing the attacker to potentially take control of their accounts (if an attacker has previously hijacked an administrator or editor account, he can plant a backdoor to regain access back).

Recommendations for Improved Security

To mitigate the risk associated with CVE-2024-0561 and similar vulnerabilities related to Stored XSS, the following recommendations are provided:

  • Update the Ultimate Posts Widget plugin to the latest patched version provided by the plugin developer, which should include proper input validation and output escaping mechanisms.
  • Implement strict input validation and output escaping in all WordPress plugins and themes to prevent XSS attacks.
  • Educate developers about secure coding practices, including the importance of sanitizing user input and properly escaping output.
  • Regularly audit and review code for vulnerabilities, including XSS vulnerabilities, as part of the development process.
  • Consider using security plugins or web application firewalls (WAFs) to monitor and block XSS attacks and other malicious activity.
  • Stay informed about emerging security threats and best practices in WordPress security by participating in security communities and following reputable security resources.

By following these recommendations, website administrators can strengthen the security of their WordPress websites and reduce the risk of exploitation through Stored XSS vulnerabilities in plugins like Ultimate Posts Widget.

#WordPressSecurity #StoredXSS #WebsiteSafety #StayProtected #HighVulnerability

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CVE-2024-0561 – Ultimate Posts Widget – Stored XSS – POC

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