NukeViet CMS is a multi Content Management System. Versions 4.5.07 and prior contain a Stored Cross-Site Scripting (XSS) vulnerability caused by insufficient server-side input sanitization in the Request class. The application relies primarily on client-side filtering to sanitize HTML tags and attributes in user-submitted content, which can be bypassed by intercepting and modifying HTTP requests directly (e.g., using Burp Suite). An attacker can inject malicious payloads which are stored server-side and executed in the browser of any user who views the content. Anyone viewing user-submitted content (such as administrators and moderators reviewing contact messages or comments) is impacted, and the vulnerability can be exploited by any anonymous visitor without authentication, with the Contact module used only as a proof of concept. Potential consequences include session hijacking through cookie theft, unauthorized actions performed under the victim's identity, defacement or redirection to phishing pages, and phishing attacks via manipulated email notifications. This issue has been fixed in version 4.5.08. If developers are unable to upgrade immediately, they should work around this issue by implementing server-side HTML sanitization in the Request class to strip or encode dangerous tags and attributes (e.g., <iframe>, srcdoc, event handlers like onerror/onload), enforcing a Content Security Policy (CSP) to restrict inline script execution, and set cookies with the HttpOnly flag to mitigate cookie theft via XSS.