CVE-2009-4074 in Internet Explorer
Summary
by MITRE
The XSS Filter in Microsoft Internet Explorer 8 allows remote attackers to leverage the "response-changing mechanism" to conduct cross-site scripting (XSS) attacks against web sites that have no inherent XSS vulnerabilities, related to the details of output encoding and improper modification of an HTML attribute, aka "XSS Filter Script Handling Vulnerability."
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/28/2021
The vulnerability described in CVE-2009-4074 represents a critical flaw in Microsoft Internet Explorer 8's cross-site scripting filter implementation that fundamentally undermines the browser's security protections. This issue specifically targets the XSS filter's response-changing mechanism, which is designed to prevent malicious scripts from executing in web applications. The vulnerability arises from the improper handling of HTML attribute modifications during the filtering process, creating a scenario where attackers can bypass the security controls even on websites that do not inherently contain XSS vulnerabilities. The flaw demonstrates a sophisticated understanding of how browser security mechanisms can be subverted through careful manipulation of the filtering logic itself rather than targeting the underlying application weaknesses.
The technical exploitation of this vulnerability occurs through the manipulation of HTML attributes within the browser's response processing pipeline. When Internet Explorer 8 encounters certain malformed HTML content, the XSS filter attempts to modify or remove potentially dangerous attributes to prevent script execution. However, the implementation contains a logic flaw where the filter's response-changing mechanism can be manipulated to alter the HTML structure in ways that circumvent the intended security boundaries. This creates a condition where the filter itself becomes a vector for attack rather than a protective mechanism. The vulnerability is particularly dangerous because it operates at the browser level, affecting all websites regardless of their individual security implementations, making it a widespread concern across the web ecosystem.
The operational impact of this vulnerability extends far beyond typical XSS attack scenarios, as it allows attackers to conduct sophisticated cross-site scripting attacks against any website that relies on IE8's built-in XSS filtering for protection. This creates a situation where even well-secured applications become vulnerable to attacks that exploit the browser's own security mechanisms. The vulnerability affects the fundamental trust model of web security, where users expect that modern browsers with built-in XSS protection will safeguard them against malicious content. Attackers can leverage this flaw to inject malicious scripts that execute in the context of legitimate websites, potentially leading to session hijacking, data theft, and privilege escalation attacks. The impact is particularly severe in enterprise environments where IE8 was widely deployed and where users might be browsing multiple applications that all rely on the browser's XSS protection mechanisms.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate security gap and the broader implications for web application security. Organizations should implement comprehensive browser security policies that either disable the vulnerable XSS filter functionality or deploy additional client-side security controls. The recommended solution involves upgrading to newer browser versions that contain fixed implementations of the XSS filtering mechanism, as Microsoft released patches for this vulnerability in subsequent updates. Security professionals should also consider implementing additional layers of protection such as Content Security Policy headers, proper input validation on server-side applications, and web application firewalls to provide defense-in-depth against exploitation attempts. This vulnerability highlights the importance of not relying solely on browser-based security mechanisms and demonstrates how even security features designed to protect users can themselves become attack vectors when improperly implemented. The issue aligns with CWE-79 which describes cross-site scripting vulnerabilities, and represents a specific instance of how improper input handling and output encoding can lead to security bypass scenarios. From an ATT&CK framework perspective, this vulnerability maps to techniques involving web-based attacks and client-side exploitation, emphasizing the need for comprehensive browser security management and the importance of keeping client-side security mechanisms up to date.