CVE-2011-2931 in Ruby on Rails
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in the strip_tags helper in actionpack/lib/action_controller/vendor/html-scanner/html/node.rb in Ruby on Rails before 2.3.13, 3.0.x before 3.0.10, and 3.1.x before 3.1.0.rc5 allows remote attackers to inject arbitrary web script or HTML via a tag with an invalid name.
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Analysis
by VulDB Data Team • 11/18/2021
The CVE-2011-2931 vulnerability represents a critical cross-site scripting flaw within the Ruby on Rails web application framework that specifically targets the strip_tags helper functionality. This vulnerability exists in the html-scanner component of actionpack, which is responsible for processing HTML content and sanitizing user input to prevent malicious code injection. The flaw is particularly concerning because it affects multiple versions of the Rails framework including 2.3.x series before 2.3.13, 3.0.x series before 3.0.10, and 3.1.x series before 3.1.0.rc5, indicating a widespread impact across different Rails releases. The vulnerability stems from inadequate validation of HTML tag names during the sanitization process, allowing attackers to bypass security measures that should prevent malicious script execution.
The technical implementation of this vulnerability occurs within the html/node.rb file where the strip_tags helper processes HTML content. When the helper encounters a tag with an invalid name, the sanitization logic fails to properly handle this edge case, creating a window for malicious input to slip through the security filters. This flaw specifically exploits the way the HTML scanner handles malformed tags, where invalid tag names can be crafted to contain executable script content that bypasses the intended sanitization. The vulnerability is categorized under CWE-79 as a Cross-Site Scripting attack, which is one of the most prevalent and dangerous web application security flaws. Attackers can leverage this weakness by crafting HTML input containing tags with malformed names that contain embedded JavaScript or HTML payload, allowing them to execute arbitrary code in the context of a victim's browser session.
The operational impact of CVE-2011-2931 is significant for any web application built on affected versions of Ruby on Rails, as it provides remote attackers with the capability to perform session hijacking, defacement, data theft, and other malicious activities. When exploited, this vulnerability allows attackers to inject malicious scripts that can steal user cookies, redirect users to phishing sites, or manipulate application behavior. The vulnerability is particularly dangerous because it operates at the input sanitization layer, meaning that even if applications properly validate user input elsewhere, the strip_tags helper can be bypassed to deliver malicious payloads. This creates a scenario where applications may appear secure from traditional input validation attacks but remain vulnerable to XSS through this specific sanitization bypass. The attack vector is straightforward, requiring only that an attacker be able to submit HTML content that gets processed through the vulnerable strip_tags helper, which is common in applications that allow user-generated content or form submissions.
Organizations affected by this vulnerability should immediately implement mitigations including upgrading to patched versions of Ruby on Rails, specifically versions 2.3.13, 3.0.10, and 3.1.0.rc5 or later. The recommended approach involves thorough version checking and patch management to ensure all affected Rails installations are updated. Additionally, defensive programming practices should be implemented to avoid relying solely on the strip_tags helper for XSS protection, including implementing Content Security Policies, using proper input validation libraries, and employing multiple layers of security controls. Security teams should also conduct comprehensive code reviews to identify any custom implementations that might be vulnerable to similar patterns and establish monitoring for suspicious HTML content submissions. This vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and demonstrates the critical importance of proper HTML sanitization in web applications, particularly within frameworks that handle user input processing. The flaw underscores the necessity of comprehensive security testing and the importance of maintaining up-to-date security patches to prevent exploitation of known vulnerabilities that can lead to full system compromise.