CVE-2004-2476 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6.0 allows remote attackers to cause a denial of service (infinite loop and crash) via an IFRAME with "?" as the file source.
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Analysis
by VulDB Data Team • 05/07/2019
Microsoft Internet Explorer 6.0 contains a critical vulnerability that enables remote attackers to induce a denial of service condition through the manipulation of IFRAME elements with malformed URL parameters. This vulnerability specifically manifests when the browser encounters an IFRAME tag where the source attribute is set to a question mark character, creating an infinite loop in the browser's rendering engine that ultimately results in application crash and system unresponsiveness. The flaw resides in the browser's handling of malformed URLs within embedded frame elements, where the parser fails to properly validate or terminate processing of such malformed input sequences.
The technical implementation of this vulnerability exploits the browser's URL parsing and resource loading mechanisms within the IFRAME element processing pipeline. When Internet Explorer 6.0 encounters an IFRAME with src="?", the browser's internal URL resolution system enters an infinite loop attempting to process the malformed reference, consuming excessive CPU resources and memory allocation until the application becomes unresponsive. This behavior aligns with CWE-835, which specifically addresses infinite loops in software implementations, and demonstrates how improper input validation can lead to resource exhaustion and system instability. The vulnerability represents a classic case of insufficient input sanitization where the browser fails to properly handle edge cases in URL parsing.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged by attackers to disrupt legitimate browser operations and potentially interfere with other applications running on the same system. When exploited, the infinite loop consumes system resources and can cause cascading failures in the browser's rendering engine, affecting user productivity and potentially compromising the overall system stability. This vulnerability particularly affects enterprise environments where users may be browsing untrusted content, as the attack can be delivered through web pages that embed malicious IFRAME elements, making it a significant concern for organizations relying on Internet Explorer 6.0 for business operations. The attack vector demonstrates characteristics consistent with the ATT&CK technique T1499.004, which involves the use of resource exhaustion attacks to disrupt system availability.
Mitigation strategies for this vulnerability include immediate deployment of Microsoft security patches that address the URL parsing flaw in Internet Explorer 6.0, along with implementing browser security policies that restrict the use of potentially malicious IFRAME elements. Organizations should also consider implementing web application firewalls that can detect and block malformed URL patterns, as well as establishing user education programs to avoid visiting untrusted websites that may contain such malicious content. The vulnerability serves as a reminder of the importance of proper input validation and the need for robust error handling in browser implementations, particularly when processing user-supplied data that may be used in resource loading operations. Additionally, upgrading to more recent browser versions that have addressed this and similar vulnerabilities provides the most effective long-term solution for protecting against such attacks.