CVE-2016-2832 in Firefox
Summary
by MITRE
Mozilla Firefox before 47.0 allows remote attackers to discover the list of disabled plugins via a fingerprinting attack involving Cascading Style Sheets (CSS) pseudo-classes.
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Analysis
by VulDB Data Team • 08/23/2022
The vulnerability identified as CVE-2016-2832 represents a significant information disclosure flaw in Mozilla Firefox versions prior to 47.0 that enables remote attackers to perform fingerprinting attacks through the manipulation of Cascading Style Sheets pseudo-classes. This vulnerability falls under the category of information disclosure and specifically relates to the browser's handling of plugin states, creating a vector for attackers to infer the presence of disabled plugins on a victim's system. The flaw exploits the way Firefox renders CSS pseudo-classes when dealing with disabled plugins, allowing attackers to distinguish between enabled and disabled plugin states through subtle visual differences in rendering behavior.
The technical implementation of this vulnerability leverages CSS pseudo-classes such as :enabled and :disabled to create visual distinctions that can be measured and interpreted by an attacker's malicious code. When Firefox processes these pseudo-classes in the context of plugin elements, it inadvertently exposes information about plugin states through the rendering process. This occurs because the browser's CSS engine handles disabled plugin elements differently than enabled ones, creating observable differences in how the elements are displayed or measured. The vulnerability specifically targets the CSS pseudo-class handling mechanism, where the rendering engine's response to disabled plugin elements can be detected through timing attacks or visual measurement techniques.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables sophisticated fingerprinting capabilities that can be used to build detailed profiles of user systems. Attackers can leverage this information to tailor subsequent attacks based on the specific plugin configuration of a target system, potentially identifying the presence of security-relevant plugins or those that might be exploited through other vulnerabilities. The fingerprinting capability provides attackers with insights into the security posture of the target system, including which plugins are disabled and potentially which plugins might be vulnerable to exploitation. This information can be combined with other fingerprinting techniques to create comprehensive browser and system profiles that enhance the effectiveness of targeted attacks.
This vulnerability aligns with CWE-200, which addresses the disclosure of information to unauthorized actors, and represents a classic example of how seemingly benign web technologies can be exploited for reconnaissance purposes. From an ATT&CK framework perspective, this vulnerability corresponds to techniques used in the reconnaissance phase of an attack, specifically those involving fingerprinting and information gathering. The ability to perform fingerprinting through CSS pseudo-classes demonstrates how web browsers can inadvertently expose system information through their rendering engines. The vulnerability also relates to techniques described in ATT&CK's T1082 (System Information Discovery) and T1592 (Threat Group Tactics) where attackers gather information about target systems to inform their attack strategies.
The recommended mitigation for this vulnerability involves upgrading to Firefox version 47.0 or later, where Mozilla implemented fixes to address the CSS pseudo-class handling that was enabling the fingerprinting attack. Organizations should also consider implementing additional security measures such as browser hardening configurations, content security policies, and regular security assessments to prevent similar vulnerabilities from being exploited. Network administrators should monitor for any signs of exploitation attempts and ensure that all browser installations are kept current with the latest security patches. The fix implemented by Mozilla likely involved modifying how the browser's CSS engine processes disabled plugin elements to eliminate the observable differences that were previously exploitable through fingerprinting attacks.