CVE-2013-3909 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 through 8 allows remote attackers to read content from a different (1) domain or (2) zone via crafted characters in Cascading Style Sheets (CSS) token sequences, aka "Internet Explorer Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 06/02/2021
This vulnerability exists in Microsoft Internet Explorer versions 6 through 8 and represents a critical information disclosure flaw that exploits cross-domain security boundaries through malformed CSS token sequences. The vulnerability stems from how Internet Explorer processes CSS content, specifically when encountering crafted characters within CSS token sequences that can bypass normal security restrictions. This allows attackers to access content from different domains or security zones that should normally be restricted by the browser's security model, creating an unauthorized data access scenario that violates fundamental web security principles.
The technical mechanism behind this vulnerability involves the improper handling of CSS parsing logic within Internet Explorer's rendering engine. When the browser encounters specially crafted CSS token sequences containing specific character combinations, the parsing routine fails to properly enforce cross-domain security policies. This parsing failure creates a condition where the browser's security boundaries are effectively bypassed, allowing malicious actors to retrieve content from different domains or security zones. The flaw operates at the CSS parser level and is classified as a violation of the same-origin policy that forms the cornerstone of web security architecture. This vulnerability directly relates to CWE-200, which addresses information exposure, and represents a classic case of improper input validation in web browser components.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with the capability to perform cross-site data theft and reconnaissance activities. Attackers can leverage this flaw to access sensitive content from other domains, potentially including authentication tokens, session data, or confidential user information. The vulnerability is particularly dangerous because it operates silently in the background, allowing unauthorized data access without user interaction or obvious signs of compromise. This makes it a prime target for advanced persistent threat campaigns and data exfiltration operations where stealth is paramount. The vulnerability affects a broad range of Internet Explorer versions, making it particularly impactful in enterprise environments where older browser versions may still be in use.
Mitigation strategies for this vulnerability require immediate patching of affected Internet Explorer versions through Microsoft security updates, as the flaw was addressed in subsequent security releases. Organizations should implement comprehensive browser security policies that enforce the use of modern browser versions and disable support for legacy components that may contain similar vulnerabilities. Network monitoring should include detection of suspicious CSS content patterns that may indicate exploitation attempts, and security teams should conduct regular vulnerability assessments to identify any remaining instances of affected browser versions within their environments. This vulnerability also highlights the importance of adhering to the principle of least privilege in web browser configurations and implementing additional security layers such as content security policies to provide defense-in-depth against similar parsing-based vulnerabilities. The incident underscores the critical need for regular security updates and the dangers of maintaining outdated browser software in production environments.