CVE-2004-0284 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6.0, Outlook 2002, and Outlook 2003 allow remote attackers to cause a denial of service (CPU consumption), if "Do not save encrypted pages to disk" is disabled, via a web site or HTML e-mail that contains two null characters (%00) after the host name.
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Analysis
by VulDB Data Team • 05/07/2019
This vulnerability resides in Microsoft Internet Explorer 6.0 and Outlook 2002 and 2003 applications where a specific parsing flaw in the handling of URLs containing null characters can lead to excessive cpu consumption and ultimately system denial of service. The vulnerability specifically manifests when the "Do not save encrypted pages to disk" security setting is disabled, creating a condition where malicious web content or html email messages can trigger resource exhaustion. The technical mechanism involves the insertion of two null characters immediately following the hostname portion of a url, which causes the affected applications to enter an infinite loop during processing. This flaw represents a classic buffer manipulation issue that falls under the CWE-129 weakness category, specifically related to improper handling of input validation and resource management. The vulnerability is particularly concerning because it operates at the application layer and can be triggered through both web browsing and email client operations, making it highly accessible to remote attackers.
The operational impact of this vulnerability extends beyond simple system unresponsiveness to potentially complete system lockup or crash scenarios. When the affected applications encounter the crafted url with embedded null characters, they consume excessive cpu cycles attempting to process the malformed input, leading to denial of service conditions that can persist until the application is manually terminated or the system is rebooted. This behavior aligns with the ATT&CK technique T1499.004 which describes denial of service attacks through resource exhaustion. The vulnerability affects not only individual user systems but also enterprise environments where multiple users may be simultaneously exposed to malicious content through email or web browsing activities, potentially creating cascading service disruption across organizational networks. The specific condition requiring the "Do not save encrypted pages to disk" setting to be disabled indicates that this vulnerability exploits a security configuration rather than being a direct exploit against core application functionality.
Mitigation strategies for this vulnerability focus on both immediate protective measures and long-term security hardening approaches. The most direct solution involves enabling the "Do not save encrypted pages to disk" security setting which prevents the vulnerable code path from being executed. Additionally, administrators should implement web content filtering solutions to block or sanitize urls containing null characters before they reach user systems. Network-level protections can include implementing proxy server rules that detect and block such malformed urls. From a broader security perspective, this vulnerability underscores the importance of proper input validation and resource management in application design, aligning with security best practices outlined in the OWASP Top Ten and NIST guidelines for secure coding. Regular security updates and patch management processes should be prioritized to address similar vulnerabilities in future software releases, as this issue demonstrates the persistent nature of parsing and input validation flaws in legacy applications. Organizations should also consider implementing email security measures that can detect and neutralize potentially malicious html content before it reaches end users, particularly in environments where legacy software must continue to operate.