CVE-2011-2197 in Ruby on Rails
Summary
by MITRE
The cross-site scripting (XSS) prevention feature in Ruby on Rails 2.x before 2.3.12, 3.0.x before 3.0.8, and 3.1.x before 3.1.0.rc2 does not properly handle mutation of safe buffers, which makes it easier for remote attackers to conduct XSS attacks via crafted strings to an application that uses a problematic string method, as demonstrated by the sub method.
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Analysis
by VulDB Data Team • 01/12/2025
The vulnerability described in CVE-2011-2197 represents a critical flaw in Ruby on Rails web application framework that undermines the framework's built-in cross-site scripting protection mechanisms. This security weakness affects multiple versions of the Rails framework including 2.x versions prior to 2.3.12, 3.0.x versions prior to 3.0.8, and 3.1.x versions prior to 3.1.0.rc2. The issue specifically targets the framework's approach to handling safe buffers, which are intended to contain content that is deemed safe from XSS attacks but can be manipulated through specific string mutation techniques. The vulnerability exploits a fundamental gap in how Rails processes and validates string operations, particularly the sub method, which allows attackers to bypass the XSS prevention safeguards that should normally protect applications from malicious script injection.
The technical flaw stems from the improper handling of safe buffer mutation within Rails' content security implementation. When applications process user input through methods like sub, the framework's XSS protection logic fails to properly account for how these operations can alter the safety status of content that was previously marked as safe. This mutation process creates a scenario where attacker-controlled strings can be transformed in ways that circumvent the framework's automatic escaping mechanisms. The vulnerability is particularly dangerous because it leverages legitimate string manipulation methods that applications commonly use, making it difficult to detect and prevent through conventional security measures. The flaw operates at the core of Rails' sanitization logic, where the framework incorrectly assumes that operations on safe content will preserve its safe status, when in reality specific string transformations can introduce malicious payloads that were not present in the original input.
The operational impact of this vulnerability is severe for any Ruby on Rails application running affected versions, as it allows remote attackers to execute arbitrary JavaScript code in the context of victim browsers. This enables a wide range of malicious activities including session hijacking, credential theft, data exfiltration, and redirection to malicious sites. The attack vector is particularly insidious because it requires minimal privileges and can be executed through normal application interaction patterns, making it difficult for administrators to detect unusual behavior. Applications that process user input through string manipulation methods like sub, gsub, or similar operations are at risk, especially those that rely on Rails' automatic XSS protection features. The vulnerability essentially neutralizes the framework's security defenses, forcing developers to implement additional manual protections or upgrade their applications to patched versions.
Organizations affected by this vulnerability should immediately prioritize upgrading their Ruby on Rails applications to versions that contain the necessary security patches. The recommended remediation involves moving to Rails 2.3.12, 3.0.8, or 3.1.0.rc2 and later versions where the XSS prevention logic has been properly enhanced to handle safe buffer mutations correctly. Security teams should conduct comprehensive code reviews to identify all instances where string manipulation methods might be processing user input, particularly focusing on methods that could potentially mutate safe content. Additionally, implementing proper input validation and output encoding at multiple layers of the application architecture provides defense-in-depth protection. The vulnerability aligns with CWE-79 Cross-site Scripting and follows ATT&CK techniques related to command and control through web application exploitation, specifically targeting the execution phase where malicious code is injected into web applications to compromise user sessions and data integrity.