CVE-2006-3869 in Internet Explorer
Summary
by MITRE
Heap-based buffer overflow in URLMON.DLL in Microsoft Internet Explorer 6 SP1 on Windows 2000 and XP SP1, with versions the MS06-042 patch before 20060824, allows remote attackers to cause a denial of service (crash) or execute arbitrary code via a long URL on a website that uses HTTP 1.1 compression.
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Analysis
by VulDB Data Team • 01/13/2025
The vulnerability identified as CVE-2006-3869 represents a critical heap-based buffer overflow within the URLMON.DLL component of Microsoft Internet Explorer 6 Service Pack 1 running on Windows 2000 and Windows XP Service Pack 1 systems. This flaw specifically manifests when Internet Explorer processes HTTP 1.1 compressed content, creating a dangerous condition where maliciously crafted URLs can trigger memory corruption. The vulnerability is particularly concerning as it affects systems that were widely deployed in enterprise environments during the mid-2000s era, making it a significant target for exploitation by threat actors seeking to compromise user systems.
The technical implementation of this vulnerability resides in the improper handling of URL length validation within the URLMON.DLL library, which is responsible for managing uniform resource locators and web content retrieval in Internet Explorer. When a user visits a malicious website containing a specially crafted URL exceeding normal length parameters, the HTTP 1.1 compression mechanism triggers a buffer overflow condition in the heap memory allocation. This occurs because the application fails to properly validate input length before copying URL data into fixed-size buffers, allowing attackers to overwrite adjacent memory locations with controlled data. The vulnerability is categorized under CWE-121 as a heap-based buffer overflow, which directly maps to the attack pattern described in the MITRE ATT&CK framework under T1203 for legitimate program execution and T1059 for command and scripting interpreter techniques.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass full arbitrary code execution capabilities, making it a severe security risk for affected systems. When exploited successfully, attackers can cause Internet Explorer to crash or, more dangerously, execute malicious code with the privileges of the logged-in user, potentially leading to complete system compromise. The vulnerability's exploitation requires a remote attacker to craft a malicious website containing a URL that triggers the buffer overflow condition during HTTP 1.1 compression processing, making it particularly effective in phishing campaigns or drive-by download scenarios. Systems that had not yet received the MS06-042 security patch released in August 2006 remained vulnerable, creating a window of opportunity for exploitation that could persist for months after the patch's availability.
Mitigation strategies for this vulnerability should focus on immediate patch deployment as the primary defense mechanism, ensuring that all affected systems receive the MS06-042 update released by Microsoft. Organizations should also implement network-level protections such as web application firewalls and URL filtering mechanisms to block access to known malicious domains. Browser hardening measures including disabling unnecessary features like HTTP 1.1 compression for untrusted sites and implementing strict content security policies can provide additional defense layers. Security monitoring should include detection of unusual Internet Explorer crash patterns and memory corruption events that may indicate exploitation attempts. The vulnerability's classification under CWE-121 and its mapping to ATT&CK techniques emphasize the importance of comprehensive security measures that address both the immediate exploitation vector and broader defensive postures against similar heap-based buffer overflow attacks that remain prevalent in modern exploit toolkits.