CVE-2001-0724 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.5 allows remote attackers to bypass security restrictions via malformed URLs that contain dotless IP addresses, which causes Internet Explorer to process the page in the Intranet Zone, which may have fewer security restrictions, aka the "Zone Spoofing Vulnerability variant" of CVE-2001-0664.
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Analysis
by VulDB Data Team • 06/10/2024
The vulnerability described in CVE-2001-0724 represents a significant security flaw in Internet Explorer 5.5 that enables remote attackers to manipulate browser security zones through carefully crafted URL structures. This issue specifically exploits the browser's handling of IP address formats, creating a zone spoofing condition that can lead to unauthorized access to restricted resources. The vulnerability stems from Internet Explorer's interpretation of dotless IP addresses, which are numeric representations of IP addresses without the standard dotted decimal notation such as 16777216 instead of 127.0.0.1. When Internet Explorer encounters such malformed URLs, it incorrectly processes them within the Intranet Zone context rather than the appropriate Internet Zone, thereby bypassing security restrictions that would normally apply to external connections.
The technical implementation of this vulnerability involves the browser's URL parsing mechanism failing to properly validate IP address formats when determining security zone boundaries. In standard operation, Internet Explorer categorizes different types of URLs into distinct security zones including Internet, Intranet, Trusted Sites, and Restricted Sites, each with varying levels of security restrictions. The dotless IP address format triggers a parsing error that causes the browser to misidentify the origin of the request, effectively placing malicious content into a less restrictive security zone. This behavior creates a pathway for attackers to circumvent security controls that would otherwise prevent access to internal network resources or sensitive data, particularly when the target system has the Intranet Zone configured with fewer security restrictions than the Internet Zone.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it can enable attackers to execute various malicious activities including credential theft, data exfiltration, and unauthorized access to internal systems. When an attacker crafts a malformed URL with a dotless IP address, they can potentially access resources that should only be available within the corporate network, effectively bridging the gap between external and internal security boundaries. This vulnerability is particularly dangerous in environments where internal network resources are accessible from the internet and where the Intranet Zone has more permissive security settings. The attack vector typically involves social engineering campaigns where users are tricked into clicking malicious links that appear legitimate but contain the malformed URL structure.
This vulnerability aligns with CWE-284, which addresses improper access control issues in software systems, and represents a classic example of how improper input validation can lead to security bypass conditions. The ATT&CK framework categorizes this as a technique for privilege escalation and initial access, specifically under the domain of "T1071.004 - Application Layer Protocol: DNS" and "T1566 - Phishing" as it often involves user interaction with malicious URLs. Organizations implementing security measures should recognize that this vulnerability demonstrates the critical importance of proper URL parsing and validation, particularly in web browsers that handle multiple security contexts. The flaw also highlights the broader security principle that applications must properly validate all input, including network addresses and URLs, to prevent unexpected behavior that could be exploited by malicious actors. The vulnerability underscores the need for robust security boundaries and the importance of not relying solely on URL format validation for security decisions, as attackers can exploit parsing inconsistencies to bypass intended protections.
The remediation strategy for this vulnerability involves updating Internet Explorer to versions that properly handle dotless IP addresses and implement correct security zone determination logic. Microsoft addressed this issue in subsequent security updates, emphasizing the importance of maintaining current browser versions and applying security patches promptly. Organizations should also implement network-level controls to monitor and restrict access to internal resources based on proper authentication and authorization mechanisms rather than relying on browser security zones alone. Security awareness training for users remains critical as this vulnerability often requires user interaction through phishing campaigns or other social engineering techniques to be effectively exploited.