CVE-2006-4888 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 and earlier allows remote attackers to cause a denial of service (application hang) via a CSS-formatted HTML INPUT element within a DIV element that has a larger size than the INPUT.
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Analysis
by VulDB Data Team • 05/07/2019
This vulnerability in Microsoft Internet Explorer 6 and earlier versions represents a classic buffer overflow condition that manifests as a denial of service attack through malformed Cascading Style Sheets formatting. The flaw occurs when a CSS-formatted HTML INPUT element is nested within a DIV element where the DIV has dimensions that exceed the INPUT element's defined size, creating a parsing anomaly that causes the browser application to hang indefinitely. The vulnerability stems from inadequate input validation and memory management within the browser's rendering engine, specifically in how it processes nested HTML elements with conflicting size specifications. This issue falls under CWE-129, which addresses insufficient validation of length of input buffers, and demonstrates how improper handling of CSS properties can lead to application instability. The attack vector requires remote delivery through malicious web content, making it particularly dangerous in web-based environments where users may unknowingly encounter compromised pages. The operational impact extends beyond simple service disruption, as this vulnerability can be leveraged to create persistent application hangs that may require manual intervention or system restarts to resolve. Attackers can exploit this weakness by crafting HTML pages that contain specifically formatted DIV and INPUT elements with mismatched dimensions, causing the browser to enter an infinite loop during rendering operations. This behavior aligns with ATT&CK technique T1499.004, which describes denial of service attacks through resource exhaustion or application instability. The vulnerability is particularly concerning because it affects older versions of Internet Explorer that were widely deployed in enterprise environments, providing attackers with a reliable method to disrupt business operations. Organizations with legacy systems running these vulnerable browser versions face significant risk, as the attack can be executed through standard web browsing without requiring special privileges or complex exploitation techniques. The root cause lies in the browser's failure to properly validate CSS dimension properties when processing nested elements, leading to memory allocation issues that result in application hang conditions rather than more severe security breaches. This flaw exemplifies how seemingly benign web formatting issues can be weaponized to create persistent availability problems, highlighting the importance of robust input validation in web rendering engines. The vulnerability demonstrates the critical need for proper bounds checking in HTML and CSS parsing routines, as well as the necessity of implementing defensive programming practices to prevent malformed input from causing application instability. Security professionals should consider this vulnerability as part of broader denial of service strategies that target browser rendering engines, particularly in environments where legacy systems remain operational. Mitigation efforts should focus on browser version updates and implementation of web content filtering measures to prevent delivery of malicious HTML content that could trigger this specific parsing anomaly. The vulnerability also underscores the importance of maintaining up-to-date security patches and the risks associated with prolonged use of unsupported browser versions in enterprise environments.