CVE-2006-7066 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 6 on Windows XP SP2 allows remote attackers to cause a denial of service (crash) by creating an object inside an iframe, deleting the frame by setting its location.href to about:blank, then accessing a property of the object within the deleted frame, which triggers a NULL pointer dereference. NOTE: it was later reported that 7.0.6000.16473 and earlier are also affected.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 07/13/2021
This vulnerability resides in Microsoft Internet Explorer 6 running on Windows XP Service Pack 2 systems and represents a classic null pointer dereference flaw that can be exploited to trigger a denial of service condition. The vulnerability specifically affects how the browser handles object references within iframe elements when those frames are rapidly deleted and accessed. The flaw occurs when an attacker creates an object inside an iframe element, subsequently deletes the frame by setting its location.href property to about:blank, and then attempts to access a property of the object that existed within the deleted frame. This sequence creates a scenario where the browser attempts to dereference a null pointer, leading to an application crash and system instability. The vulnerability demonstrates a fundamental memory management issue in the browser's handling of dynamic DOM objects and their lifecycle management within iframe contexts.
The technical implementation of this vulnerability leverages the browser's object model and DOM manipulation capabilities to exploit a race condition between object creation and frame deletion. When an iframe is set to about:blank, the browser begins the process of destroying the frame's document context, but if object references remain in memory or are accessed before complete cleanup, the system attempts to access memory locations that have already been deallocated. This pattern of exploitation aligns with CWE-476 which specifically addresses NULL pointer dereference vulnerabilities, where a program attempts to access memory through a null pointer reference. The flaw represents a memory safety issue that can be consistently reproduced through controlled manipulation of the browser's rendering engine's object lifecycle management.
The operational impact of this vulnerability extends beyond simple denial of service as it can be leveraged by malicious actors to disrupt user sessions and potentially create more serious security implications. When exploited, the vulnerability causes Internet Explorer to crash and terminate the browser process, forcing users to restart their browsing sessions and potentially lose unsaved work. The vulnerability affects not only IE 6 but also IE 7 versions up to build 7.0.6000.16473, indicating a widespread issue within the browser's core architecture. From an attacker's perspective, this vulnerability fits within the ATT&CK framework's T1499.004 technique for network denial of service, as it can be used to disrupt user access to web applications and services through browser-based attacks. The exploit requires minimal privileges and can be delivered through malicious web content, making it particularly dangerous in phishing campaigns or targeted attacks.
Mitigation strategies for this vulnerability should focus on immediate browser updates and patches from Microsoft, as well as implementing browser security controls to limit the execution of potentially malicious content. Organizations should ensure that all systems are updated to the latest security patches, as Microsoft released fixes specifically addressing this vulnerability. Browser hardening techniques including disabling active scripting in restricted zones, implementing content security policies, and using sandboxing mechanisms can help reduce the impact of such exploits. Network-level protections such as web application firewalls and intrusion prevention systems can also be configured to detect and block exploitation attempts. Additionally, user education regarding safe browsing practices and avoiding untrusted websites remains crucial in preventing successful exploitation of this vulnerability, as it demonstrates the importance of maintaining current security software and understanding the risks associated with browser-based attacks that target core application functionality.