CVE-2004-2363 in PHPX
Summary
by MITRE
Validate-Before-Canonicalize vulnerability in the checkURI function in functions.inc.php in PHPX 3.0 through 3.2.6 allows remote attackers to conduct cross-site scripting (XSS) attacks via hex-encoded tags, which bypass the check for literal "<", ">", "(", and ")" characters, as demonstrated using the limit parameter to forums.php and a variety of other vectors.
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Analysis
by VulDB Data Team • 06/02/2025
The vulnerability described in CVE-2004-2363 represents a critical Validate-Before-Canonicalize flaw that fundamentally undermines the security of web applications processing user input. This weakness exists within the checkURI function located in functions.inc.php of PHPX versions 3.0 through 3.2.6, where the application performs input validation before canonicalizing the data, creating a window of opportunity for attackers to bypass security measures through encoded payload delivery. The flaw specifically targets the validation logic that is designed to block literal characters such as "<", ">", "(", and ")" which are commonly used in cross-site scripting attacks. However, the vulnerability allows malicious actors to exploit this gap by employing hex-encoded versions of these characters, effectively circumventing the intended protection mechanisms that would normally prevent such dangerous inputs from being processed.
The technical execution of this vulnerability demonstrates sophisticated attack methodology that leverages encoding techniques to evade detection systems. Attackers can manipulate the limit parameter in forums.php and other application vectors to inject malicious payloads that appear harmless during initial validation but are decoded and executed during subsequent processing. This particular vulnerability operates under the CWE-185 weakness category, specifically addressing improper input handling and canonicalization issues that occur before validation, creating a dangerous scenario where input validation becomes ineffective against encoded malicious content. The attack chain typically involves encoding dangerous characters using hex encoding, submitting these encoded values through web forms or URL parameters, and then exploiting the application's failure to properly canonicalize the data before validation, allowing the malicious content to pass through security checks undetected.
The operational impact of CVE-2004-2363 extends beyond simple cross-site scripting capabilities to potentially enable full session hijacking, data theft, and unauthorized administrative actions within affected applications. When exploited successfully, this vulnerability allows remote attackers to inject malicious scripts that can execute in the context of authenticated users' browsers, potentially leading to complete compromise of user sessions and sensitive data exposure. The vulnerability's persistence across multiple versions of PHPX indicates a fundamental design flaw in the input handling architecture that could affect numerous applications implementing this framework. Organizations running affected versions face significant risk of user data compromise, application integrity violations, and potential regulatory compliance issues, particularly in environments where user-generated content is processed and stored. The vulnerability's classification under ATT&CK technique T1566.001 (Phishing with Malicious Attachments) and T1566.002 (Phishing with Malicious Links) reflects its capability to facilitate social engineering attacks that leverage the XSS vulnerability for broader exploitation campaigns.
Mitigation strategies for CVE-2004-2363 require immediate implementation of proper input canonicalization before validation, ensuring that all user-provided data is normalized and decoded before any security checks are performed. Organizations should implement comprehensive input sanitization routines that account for multiple encoding methods, including hex, octal, and URL encoding, rather than relying solely on literal character detection. The recommended approach involves upgrading to patched versions of PHPX or implementing custom input validation that canonicalizes data prior to validation checks, as specified in the OWASP Input Validation Cheat Sheet and the CERT/CC Secure Coding Guidelines. Additionally, implementing Content Security Policy (CSP) headers, output encoding for all dynamic content, and regular security audits of input handling functions can significantly reduce the attack surface and prevent exploitation of similar vulnerabilities. The vulnerability's remediation should also include comprehensive testing of all input vectors, particularly those involving parameter manipulation and user content submission, to ensure that canonicalization occurs before any validation logic is executed.