CVE-2007-1094 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 7 allows remote attackers to cause a denial of service (NULL dereference and application crash) via JavaScript onUnload handlers that modify the structure of a document.
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Analysis
by VulDB Data Team • 05/07/2019
Microsoft Internet Explorer 7 suffered from a critical vulnerability that enabled remote attackers to execute denial of service attacks through carefully crafted JavaScript code targeting the onUnload event handlers. This vulnerability stemmed from improper handling of document structure modifications during the browser's unload process, creating a NULL dereference condition that resulted in application crashes and complete service disruption for affected users.
The technical flaw occurred when JavaScript code executed within onUnload handlers attempted to modify document structure elements while the browser was in the process of tearing down the document object model. This race condition between document modification and cleanup operations created a scenario where memory references became invalid or null, leading to a NULL pointer dereference that terminated the browser process entirely. The vulnerability specifically exploited the browser's failure to properly validate document structure modifications during the unload sequence, allowing attackers to inject malicious JavaScript that would trigger the crash condition.
This vulnerability had significant operational impact on users and organizations relying on Internet Explorer 7, as it could be exploited through various attack vectors including malicious websites, email attachments, or compromised web services. The denial of service nature of the vulnerability meant that users could be suddenly disconnected from web applications, potentially losing unsaved work or interrupting critical business processes. Organizations faced increased support costs due to user disruptions and the need for emergency patches or browser upgrades to maintain service availability.
The vulnerability aligns with CWE-476 which addresses NULL pointer dereference conditions in software implementations. From an adversarial perspective, this flaw mapped to ATT&CK technique T1499.004 which covers network denial of service attacks through application layer exploitation. The attack required minimal privileges and could be executed remotely, making it particularly dangerous for enterprise environments where users might encounter malicious content through web browsing or email.
Mitigation strategies included applying Microsoft's security patches and updates released in response to this vulnerability, as well as implementing browser security configurations that restricted JavaScript execution during unload events. Organizations should have considered deploying browser isolation solutions or using alternative browsers that were not affected by this specific vulnerability. Additionally, user education regarding safe browsing practices and the importance of keeping software updated became critical components of the overall security posture to prevent exploitation of such vulnerabilities.