CVE-2013-4891 in CodeIgniter
Summary
by MITRE
The xss_clean function in CodeIgniter before 2.1.4 might allow remote attackers to bypass an intended protection mechanism and conduct cross-site scripting (XSS) attacks via an unclosed HTML tag.
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Analysis
by VulDB Data Team • 02/08/2023
The CVE-2013-4891 vulnerability resides within the xss_clean function of CodeIgniter framework versions prior to 2.1.4, representing a critical security flaw that undermines the application's intended cross-site scripting protection mechanisms. This vulnerability specifically targets the framework's input sanitization capabilities, which are designed to prevent malicious script injection attacks by filtering out potentially dangerous HTML and JavaScript content. The flaw manifests when the xss_clean function fails to properly handle unclosed HTML tags, allowing attackers to craft malicious payloads that bypass the security checks. The vulnerability's impact extends beyond simple bypass mechanisms as it directly compromises the core security model that developers rely upon when implementing input validation in web applications.
The technical nature of this vulnerability stems from insufficient parsing logic within the xss_clean function's HTML tag handling routine. When encountering unclosed HTML tags, the sanitization process fails to properly identify and neutralize the malicious content that follows these tags. This parsing deficiency creates a window where attackers can inject script code that appears to be valid HTML but contains embedded malicious payloads. The vulnerability specifically exploits the function's inability to properly close or validate HTML tag structures, allowing attackers to inject malformed HTML that the sanitization process does not adequately address. This flaw operates at the level of HTML entity and tag parsing, where the function's logic does not account for edge cases involving improperly closed tags that could contain script content.
The operational impact of CVE-2013-4891 is substantial as it allows remote attackers to execute cross-site scripting attacks against users of vulnerable CodeIgniter applications. This vulnerability enables attackers to inject malicious scripts that can steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The attack surface is broad since CodeIgniter is widely used for web application development, and the vulnerability affects applications that rely on the framework's built-in XSS protection mechanisms. Attackers can exploit this vulnerability through various input vectors including form submissions, URL parameters, and API endpoints where user input is processed through the xss_clean function. The vulnerability's persistence across multiple application types makes it particularly dangerous as it can affect content management systems, web applications, and any platform utilizing the affected CodeIgniter versions.
The mitigation strategy for CVE-2013-4891 involves immediate upgrade to CodeIgniter version 2.1.4 or later, which contains the patched xss_clean function with improved HTML tag handling logic. Organizations should also implement additional security measures including input validation at multiple layers, comprehensive testing of sanitization functions, and regular security audits of web applications. The vulnerability aligns with CWE-79, which describes cross-site scripting flaws in web applications, and represents a classic example of inadequate input validation. From an ATT&CK framework perspective, this vulnerability maps to technique T1190, known as "Exploit Public-Facing Application," and T1210, "Exploitation of Remote Services," as attackers can leverage this flaw to compromise web applications. Organizations should also consider implementing web application firewalls and additional security controls beyond the framework's built-in protections to create defense-in-depth strategies against similar vulnerabilities.
This vulnerability demonstrates the critical importance of robust HTML parsing and sanitization in web application security frameworks. The flaw underscores the necessity of comprehensive testing for edge cases in security functions and highlights how seemingly minor parsing issues can create significant security vulnerabilities. The incident emphasizes the need for continuous security updates and the importance of maintaining current versions of web application frameworks to protect against known vulnerabilities. Security teams should prioritize regular vulnerability assessments and ensure that all dependencies and frameworks are kept up to date with the latest security patches to prevent exploitation of similar flaws in the future.