CVE-2019-15587 in Loofah Gem
Summary
by MITRE • 01/25/2023
In the Loofah gem for Ruby through v2.3.0 unsanitized JavaScript may occur in sanitized output when a crafted SVG element is republished.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability identified as CVE-2019-15587 affects the Loofah gem version 2.3.0 and earlier, representing a critical security flaw in Ruby applications that process HTML and XML content. This issue stems from insufficient sanitization of SVG elements within the gem's HTML purification mechanisms, creating a potential vector for cross-site scripting attacks. The vulnerability specifically manifests when crafted SVG elements containing malicious JavaScript are processed through Loofah's sanitization functions, resulting in the unintended execution of harmful code in contexts where sanitized output is expected. The flaw impacts web applications that rely on Loofah to clean user-generated content, potentially exposing systems to unauthorized code execution and data breaches.
The technical root cause of this vulnerability lies in Loofah's inadequate handling of SVG namespace declarations and element attributes during the sanitization process. When processing SVG content, the gem fails to properly validate or strip JavaScript event handlers and other potentially dangerous attributes that could be embedded within SVG elements. This weakness allows attackers to embed malicious code within SVG graphics that are subsequently rendered in web browsers, bypassing traditional HTML sanitization controls. The vulnerability operates at the intersection of HTML5 and SVG parsing standards, where the gem's implementation does not adequately distinguish between legitimate SVG attributes and those that could contain executable JavaScript code. This issue falls under the CWE-79 category of Cross-Site Scripting, specifically representing a variant where SVG elements serve as the attack vector.
The operational impact of CVE-2019-15587 extends beyond simple code execution, potentially enabling attackers to perform session hijacking, data exfiltration, and full system compromise through browser-based attacks. Applications utilizing Loofah for content sanitization in web frameworks such as Ruby on Rails become vulnerable to attacks that could lead to unauthorized access to user accounts, modification of sensitive data, or complete system infiltration. The vulnerability is particularly concerning because SVG elements are commonly used in modern web applications for graphics and user interfaces, making the attack surface broader than traditional HTML-based XSS vulnerabilities. Attackers can exploit this weakness by embedding malicious SVG content in user-generated posts, comments, or file uploads, which then gets processed and displayed to other users, creating a persistent threat vector.
Mitigation strategies for CVE-2019-15587 require immediate patching of the Loofah gem to version 2.3.1 or later, which contains the necessary fixes for proper SVG sanitization. Organizations should also implement additional defensive measures including content security policies, input validation, and regular security scanning of web applications. The remediation process should include thorough testing of all applications that utilize Loofah, particularly those handling user-generated content or external data feeds. Security teams should monitor for any potential exploitation attempts and consider implementing web application firewalls to detect and block malicious SVG content. This vulnerability highlights the importance of comprehensive sanitization routines that account for the complex interplay between HTML, XML, and SVG standards, aligning with ATT&CK technique T1211 for exploitation of input validation weaknesses in web applications. Organizations should also review their dependency management practices to ensure timely patching of security vulnerabilities across all application components.