CVE-2002-1186 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.01 through 6.0 does not properly perform security checks on certain encoded characters within a URL, which allows a remote attacker to steal potentially sensitive information from a user by redirecting the user to another site that has that information, aka "Encoded Characters Information Disclosure."
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Analysis
by VulDB Data Team • 04/07/2017
The vulnerability identified as CVE-2002-1186 represents a critical security flaw in Microsoft Internet Explorer versions 5.01 through 6.0 that fundamentally undermines the browser's ability to properly validate URL encoding. This weakness stems from the browser's inadequate handling of encoded characters within Uniform Resource Locators, creating a pathway for malicious actors to exploit the security boundaries that should protect user data and session information. The flaw operates by allowing attackers to craft specially formatted URLs that bypass the browser's intended security mechanisms, effectively undermining the trust model that web browsers establish between users and websites.
The technical implementation of this vulnerability involves the browser's failure to properly decode and validate URL components before establishing connections to remote servers. When Internet Explorer encounters encoded characters within a URL, it does not consistently apply the same security checks that would normally occur during standard URL parsing. This inconsistency allows attackers to construct malicious URLs where encoded characters are processed in ways that can reveal sensitive information from the user's browser session or redirect to sites that can harvest potentially confidential data. The vulnerability specifically targets the way the browser handles character encoding within URL strings, creating a mismatch between the expected security behavior and the actual implementation.
From an operational perspective, this vulnerability creates significant risks for users who may unknowingly navigate to maliciously crafted URLs that appear legitimate but contain encoded characters designed to exploit the security gap. The attack vector typically involves social engineering techniques where users are directed to seemingly benign websites that contain hidden encoded URLs. These URLs can potentially access information from other domains that the user has legitimate access to, including cookies, session information, or other sensitive data that should remain protected by the browser's security model. The impact extends beyond simple information disclosure, as it can potentially enable more sophisticated attacks such as session hijacking or cross-site request forgery exploitation.
The security implications of CVE-2002-1186 align with CWE-20, which describes improper input validation, and can be mapped to ATT&CK technique T1566 for social engineering attacks. Organizations using affected Internet Explorer versions face heightened risk of data breaches and unauthorized access to sensitive information. The vulnerability demonstrates the critical importance of proper URL validation and encoding handling in web browsers, as it shows how seemingly minor implementation flaws can create significant security risks. This particular vulnerability highlights the need for comprehensive security testing of URL parsing mechanisms and underscores the importance of maintaining up-to-date browser software to protect against known security flaws.
Mitigation strategies for this vulnerability primarily involve immediate browser updates to versions that address the URL encoding validation issue, along with implementing network-level controls to filter potentially malicious URLs. Organizations should also consider deploying web application firewalls and implementing strict URL validation policies to prevent exploitation. User education remains crucial, as many attacks leveraging this vulnerability rely on social engineering to convince users to navigate to malicious sites. The vulnerability serves as a historical example of how browser security implementations must account for complex encoding scenarios and demonstrates the critical need for thorough security testing of core browser functionality that handles user input and network communications.