CVE-2011-2670 in Firefox
Summary
by MITRE
Mozilla Firefox before 3.6 is vulnerable to XSS via the rendering of Cascading Style Sheets
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Analysis
by VulDB Data Team • 04/22/2023
The vulnerability identified as CVE-2011-2670 represents a cross-site scripting flaw in Mozilla Firefox versions prior to 3.6, specifically related to the browser's handling of Cascading Style Sheets during document rendering processes. This issue arises from insufficient input validation and sanitization mechanisms within Firefox's CSS processing engine, creating an avenue for malicious actors to inject and execute arbitrary script code within the context of a user's browsing session. The vulnerability demonstrates a classic example of how web browser rendering engines can be exploited through seemingly benign content manipulation, particularly when dealing with stylesheet processing.
The technical root cause of this vulnerability lies in Firefox's CSS parser implementation, which fails to properly sanitize or validate CSS content that contains embedded script references or malicious code sequences. When the browser encounters certain malformed or crafted CSS rules during the rendering phase, it processes these elements without adequate security checks, potentially executing JavaScript code embedded within CSS declarations. This processing flaw falls under the category of CWE-79 - Improper Neutralization of Input During Web Page Generation, specifically manifesting as a cross-site scripting vulnerability during content rendering operations. The vulnerability is particularly concerning because CSS is often used in web applications for presentation purposes and is frequently trusted by browsers, making it an attractive vector for attackers seeking to bypass traditional security controls.
The operational impact of CVE-2011-2670 extends beyond simple script execution, as it allows attackers to manipulate user sessions, steal sensitive information, or redirect users to malicious websites. An attacker could craft a malicious CSS file or inject malicious CSS into a web page that would execute when Firefox renders the page, potentially compromising the user's browser session and enabling further attacks. This vulnerability directly maps to ATT&CK technique T1211 - Exploitation for Defense Evasion, where attackers leverage browser vulnerabilities to maintain persistent access or evade detection mechanisms. The widespread use of Firefox 3.5 and earlier versions at the time of discovery meant that this vulnerability affected a significant user base, particularly in enterprise environments where legacy browser versions were commonly deployed.
Mitigation strategies for this vulnerability required immediate patching of Firefox installations to version 3.6 or later, which included enhanced CSS validation and sanitization mechanisms. Organizations should have implemented comprehensive browser update policies and deployed automated patch management systems to ensure all users were protected against this and similar vulnerabilities. Additionally, security teams should have monitored for exploitation attempts through network traffic analysis and implemented web application firewalls to detect and block malicious CSS content. The vulnerability highlighted the importance of maintaining up-to-date browser versions and demonstrated how seemingly innocuous components like CSS processing can become critical attack vectors requiring robust security controls and continuous monitoring.