CVE-2005-0054 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.01, 5.5, and 6 allows remote attackers to spoof a less restrictive security zone and execute arbitrary code via an HTML page containing URLs that contain hostnames that have been double hex encoded, which are decoded twice to generate a malicious hostname, aka the "URL Decoding Zone Spoofing Vulnerability."
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Analysis
by VulDB Data Team • 07/05/2025
The CVE-2005-0054 vulnerability represents a critical security flaw in Microsoft Internet Explorer versions 5.01, 5.5, and 6.0 that enables remote attackers to bypass security zone restrictions through carefully crafted URL encoding techniques. This vulnerability specifically targets the browser's URL decoding mechanism, creating a pathway for attackers to manipulate how the browser interprets and processes web addresses. The flaw exploits the way Internet Explorer handles double-encoded hostnames, where maliciously crafted URLs can be decoded twice to generate unexpected and potentially harmful hostnames that the browser treats as belonging to a less restrictive security zone.
The technical implementation of this vulnerability relies on the browser's failure to properly validate and normalize URL components during the decoding process. When an attacker crafts a URL with a hostname that has been double hex encoded, the initial decoding process transforms the encoded characters into a format that appears legitimate to the browser's security model. However, the second decoding operation reveals the true malicious hostname, which the browser incorrectly interprets as originating from a trusted domain or security zone. This creates a scenario where a malicious page can appear to come from a trusted source while simultaneously executing code with elevated privileges. The vulnerability operates at the intersection of web browser security architecture and URL parsing mechanisms, demonstrating how improper handling of encoded data can lead to privilege escalation and zone spoofing attacks.
The operational impact of this vulnerability is severe as it allows attackers to circumvent fundamental security protections that separate trusted and untrusted web content. An attacker can create a malicious HTML page that, when loaded by an affected browser, appears to originate from a trusted domain while simultaneously executing arbitrary code with the privileges associated with the less restrictive security zone. This effectively undermines the browser's security model, potentially allowing for session hijacking, credential theft, and other malicious activities. The vulnerability is particularly dangerous because it can be exploited through standard web browsing activities, requiring no special privileges or tools from the attacker beyond the ability to host malicious content on a web server. The attack vector demonstrates a classic case of how improper input validation can lead to security bypasses, with the vulnerability being classified under CWE-180, which addresses improper handling of encoded data.
Mitigation strategies for CVE-2005-0054 require immediate patching of affected Internet Explorer versions or deployment of alternative security measures. Microsoft released security updates that addressed the URL decoding behavior and improved validation of encoded hostnames in affected browser versions. Organizations should implement comprehensive browser security policies that disable potentially dangerous features and ensure all systems are running patched versions of Internet Explorer. Network-level protections such as web application firewalls and content filtering solutions can provide additional layers of defense by inspecting and blocking suspicious URL patterns. The vulnerability also highlights the importance of proper input validation and normalization in security-critical applications, aligning with ATT&CK technique T1059 for execution through command-line interfaces and T1190 for exploitation of remote services. Security teams should also consider implementing monitoring for suspicious URL patterns and browser behavior that could indicate exploitation attempts, as this vulnerability represents a classic example of how encoding manipulation can be used to bypass security controls.