CVE-2002-2436 in Firefox
Summary
by MITRE
The Cascading Style Sheets (CSS) implementation in Mozilla Firefox before 4.0, Thunderbird before 3.3, and SeaMonkey before 2.1 does not properly handle the :visited pseudo-class, which allows remote attackers to obtain sensitive information about visited web pages via a crafted HTML document, a related issue to CVE-2010-2264.
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Analysis
by VulDB Data Team • 02/13/2019
The vulnerability described in CVE-2002-2436 represents a significant security flaw in the CSS implementation of major web browsers including Mozilla Firefox, Thunderbird, and SeaMonkey. This issue specifically targets the handling of the :visited pseudo-class, which is a CSS selector that allows styling of links that have been visited by the user. The flaw enables malicious actors to exploit the browser's rendering engine to infer whether a user has visited specific web pages, thereby compromising user privacy and potentially exposing sensitive browsing history information.
The technical nature of this vulnerability stems from the improper implementation of CSS pseudo-classes in the browser's rendering engine, particularly how it processes the :visited selector. When a web page contains crafted HTML code that utilizes the :visited pseudo-class, the browser should ideally prevent scripts from determining the visited status of links through visual styling or JavaScript access. However, the flaw in these older browser versions allowed attackers to bypass these security mechanisms, creating a potential information disclosure channel. The vulnerability operates by leveraging the ability of CSS to access certain visual properties of visited links, which can then be read by JavaScript through techniques such as element measurement or color detection, ultimately revealing user browsing patterns.
This security issue carries substantial operational impact as it enables attackers to perform tracking and surveillance activities without user consent. The vulnerability is particularly concerning because it allows remote attackers to determine whether users have visited specific web pages, which could include sensitive content such as medical sites, financial institutions, or personal communication platforms. The attack vector involves crafting malicious HTML documents that contain specially designed CSS rules to probe visited link states, potentially exposing private browsing habits and user behavior patterns. This type of information disclosure can be particularly damaging when combined with other tracking techniques, as it provides attackers with detailed insights into user activities and preferences.
The vulnerability aligns with CWE-200, which covers information exposure, and represents a classic example of how browser security mechanisms can be subverted to reveal user data. From an ATT&CK framework perspective, this vulnerability maps to techniques involving information gathering and credential access, as it enables adversaries to collect sensitive information about user activities. The flaw demonstrates the importance of proper isolation between CSS styling and JavaScript execution in web browsers, as well as the need for comprehensive security testing of CSS implementation features. Organizations should prioritize updating affected browser versions to mitigate this risk, as the vulnerability affects widely used applications including email clients and web browsers. Additionally, users should be educated about the risks of visiting untrusted websites and the importance of keeping software updated to protect against such information disclosure attacks.
This vulnerability highlights the broader challenge of maintaining web browser security in the face of complex CSS implementations and the potential for seemingly innocuous styling features to become security attack vectors. The issue serves as a reminder of the critical need for comprehensive security testing of browser features and the importance of implementing robust isolation mechanisms between different browser components to prevent cross-component information leakage. The remediation approach requires immediate software updates to affected versions, with security patches specifically addressing the CSS pseudo-class handling behavior to prevent unauthorized access to visited link information.