CVE-2008-4127 in Internet Explorer
Summary
by MITRE
Mshtml.dll in Microsoft Internet Explorer 7 Gold 7.0.5730 and 8 Beta 8.0.6001 on Windows XP SP2 allows remote attackers to cause a denial of service (failure of subsequent image rendering) via a crafted PNG file, related to an infinite loop in the CDwnTaskExec::ThreadExec function.
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Analysis
by VulDB Data Team • 05/26/2025
The vulnerability identified as CVE-2008-4127 represents a critical denial of service flaw within Microsoft Internet Explorer's handling of PNG image files. This issue specifically affects Internet Explorer 7 version 7.0.5730 and Internet Explorer 8 beta version 8.0.6001 when running on Windows XP Service Pack 2 systems. The flaw resides in the mshtml.dll component which serves as the core rendering engine for web content in Internet Explorer, making it a fundamental component of the browser's functionality.
The technical root cause of this vulnerability stems from an infinite loop occurring within the CDwnTaskExec::ThreadExec function of the mshtml.dll library. When Internet Explorer encounters a specially crafted PNG file, the image processing code enters an endless execution cycle that prevents proper rendering of subsequent images on the same page or in subsequent browsing sessions. This infinite loop is triggered during the asynchronous download and processing of image resources, where the CDwnTaskExec::ThreadExec function fails to properly terminate its execution loop when processing malformed or maliciously constructed PNG data structures.
The operational impact of this vulnerability extends beyond simple browser instability, creating a persistent denial of service condition that affects user experience and potentially enabling more sophisticated attack vectors. Once a malicious PNG file is loaded, the browser becomes unresponsive to image rendering operations, requiring manual intervention through process termination or system reboot to restore normal functionality. This behavior creates a reliable method for attackers to disrupt user activities and can be particularly problematic in environments where continuous browser availability is critical.
This vulnerability aligns with CWE-835, which describes the weakness of an infinite loop or infinite recursion in software systems, and demonstrates how improper input validation can lead to resource exhaustion and system instability. The attack pattern follows techniques described in the ATT&CK framework under T1499.004 for network denial of service, where attackers exploit application-level flaws to consume system resources and render services unavailable. The vulnerability represents a classic example of how image processing libraries can become attack surfaces when they fail to properly validate input data structures, particularly in legacy browser implementations that lack modern input sanitization mechanisms.
Mitigation strategies for this vulnerability include immediate deployment of Microsoft security updates that address the specific infinite loop condition in the mshtml.dll component. Users should also implement additional protective measures such as disabling automatic image loading for untrusted content, employing content filtering solutions, and maintaining updated antivirus signatures that can detect malicious PNG files. Network administrators should consider implementing web application firewalls that can identify and block suspicious image file patterns, while organizations should conduct regular security assessments to ensure all systems are properly patched against known vulnerabilities. The incident underscores the importance of proper input validation and the need for robust error handling in multimedia processing components of web browsers.