CVE-2011-1992 in Internet Explorer
Summary
by MITRE
The XSS Filter in Microsoft Internet Explorer 8 allows remote attackers to read content from a different (1) domain or (2) zone via a "trial and error" attack, aka "XSS Filter Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 03/20/2021
The vulnerability identified as CVE-2011-1992 represents a significant information disclosure flaw within Microsoft Internet Explorer 8's cross-site scripting filter mechanism. This security weakness specifically targets the browser's attempt to protect users from malicious cross-site scripting attacks while inadvertently creating a pathway for attackers to bypass these protections. The vulnerability stems from how IE8's XSS filter handles certain input validation scenarios, particularly when processing content from different domains or security zones. Attackers can exploit this flaw through a systematic trial and error approach that leverages the browser's filtering behavior to infer information about content that should otherwise remain protected by cross-domain security policies.
The technical nature of this vulnerability operates at the intersection of web security boundaries and browser implementation flaws. When Internet Explorer 8 processes web content, its XSS filter attempts to identify and neutralize potentially malicious scripts that could compromise user sessions or steal sensitive data. However, the implementation contains a logical flaw that allows attackers to craft specific inputs that cause the filter to behave in predictable ways. Through careful analysis of the filter's responses to various inputs, malicious actors can perform a form of side-channel attack that reveals information about content from different domains or security zones. This occurs because the filter's error handling or response patterns differ when processing legitimate versus malicious content, creating observable differences that can be exploited.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally undermines the security model that separates different domains and security zones within web browsers. Users operating Internet Explorer 8 may unknowingly expose sensitive information from other domains or zones to attackers who can systematically probe the browser's behavior. The vulnerability is particularly concerning because it operates at the application layer, where attackers can leverage the browser's own protective mechanisms against it. This creates a scenario where the very security features designed to protect users become a vector for information leakage, potentially exposing session tokens, user data, or other sensitive content that should remain isolated between different security contexts.
From a cybersecurity perspective, this vulnerability aligns with CWE-200, which describes information disclosure vulnerabilities, and represents a classic example of how defensive mechanisms can introduce new attack surfaces. The attack pattern follows elements of the ATT&CK framework's technique T1071.004, which involves application layer protocol manipulation, and T1566, which encompasses credential access through various attack vectors. Organizations running Internet Explorer 8 were particularly vulnerable to this attack as it required no sophisticated exploitation techniques beyond understanding the browser's response patterns. The vulnerability demonstrates the critical importance of thorough testing of security features and the potential for defensive implementations to create new attack vectors rather than eliminate existing ones.
Mitigation strategies for this vulnerability primarily involve updating to newer versions of Internet Explorer that contain corrected XSS filtering implementations or implementing additional security controls such as proper content security policies, web application firewalls, and browser security enhancements. Microsoft addressed this issue in subsequent updates, but the vulnerability serves as a cautionary example of how security features must be rigorously tested in realistic attack scenarios to prevent unintended information disclosure. Organizations should also consider implementing security awareness training to help users recognize potential indicators of such attacks and maintain up-to-date browser versions to prevent exploitation of known vulnerabilities. The incident highlights the importance of defensive programming practices and the need for security professionals to understand not just how security mechanisms work, but how attackers might potentially abuse their behavior patterns.