CVE-2005-4260 in PHP-Nuke
Summary
by MITRE
Interpretation conflict in includes/mainfile.php in PHP-Nuke 7.9 and later allows remote attackers to perform cross-site scripting (XSS) attacks by replacing the ">" in the tag with a "<", which bypasses the regular expressions that sanitize the data, but is automatically corrected by many web browsers. NOTE: it could be argued that this vulnerability is due to a design limitation of many web browsers; if so, then this should not be treated as a vulnerability in PHP-Nuke.
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Analysis
by VulDB Data Team • 09/22/2025
The vulnerability described in CVE-2005-4260 represents a sophisticated cross-site scripting attack vector that exploits an interpretation conflict within the PHP-Nuke content management system version 7.9 and later. This flaw specifically targets the includes/mainfile.php component where input sanitization mechanisms fail to properly handle malformed HTML tag structures, creating a security gap that malicious actors can leverage to inject persistent XSS payloads. The vulnerability arises from the system's reliance on regular expression-based sanitization that does not account for browser-based automatic correction mechanisms, allowing attackers to craft payloads that bypass initial validation checks.
The technical implementation of this vulnerability demonstrates a fundamental flaw in the input validation approach used by PHP-Nuke's sanitization routines. When attackers replace the closing angle bracket ">" character with the opening bracket "<" in HTML tags, they exploit a discrepancy between the sanitization logic and how modern web browsers automatically correct malformed HTML structures. This creates a scenario where the sanitization process, which employs regular expressions to detect and neutralize potentially dangerous characters, fails to recognize the malicious payload because the replacement character combination does not match the expected patterns. However, browsers automatically correct this malformed syntax during rendering, effectively executing the XSS payload in the victim's browser context.
The operational impact of this vulnerability extends beyond simple script injection, as it enables attackers to perform session hijacking, defacement of web pages, and data exfiltration from authenticated user sessions. The automatic correction behavior of web browsers means that victims may not immediately recognize the malicious nature of the content, as the browser renders the corrected version while the underlying XSS payload remains active. This creates a stealthy attack vector that can persist across multiple user interactions and potentially compromise sensitive information from users who view affected content. The vulnerability affects the core application functionality since it operates at the main file inclusion level, potentially impacting all user-facing components that rely on the sanitized input processing.
Security professionals should consider this vulnerability through the lens of CWE-79, which specifically addresses cross-site scripting flaws in web applications, and the broader ATT&CK framework's T1566 category for initial access through spearphishing. The design limitation mentioned in the vulnerability description highlights the importance of robust input validation that does not rely on browser behavior for security enforcement. Organizations should implement multiple layers of defense including proper HTML escaping, Content Security Policy implementation, and comprehensive input validation that accounts for various encoding and transformation techniques. Additionally, the vulnerability underscores the necessity of avoiding reliance on client-side behavior for security controls, as demonstrated by the ATT&CK technique T1210 which covers exploitation of weaknesses in input sanitization processes.
The remediation approach should focus on strengthening the input sanitization mechanism within PHP-Nuke to properly handle all variations of HTML tag structures, including malformed combinations that browsers might automatically correct. This involves implementing more comprehensive regular expression patterns that account for the various character substitutions attackers might employ, as well as adopting a whitelist-based approach to input validation rather than relying solely on blacklisting techniques. Organizations should also consider implementing proper HTML entity encoding for all user-supplied content and ensuring that the application's security model does not depend on browser-based automatic corrections for maintaining security boundaries. The vulnerability serves as a cautionary example of why security controls must be robust against all possible attack vectors, regardless of how browsers might interpret malformed content, and why security measures should be validated through comprehensive testing rather than relying on browser behavior for protection.