CVE-2018-3740 in Sanitize Gem
Summary
by MITRE
A specially crafted HTML fragment can cause Sanitize gem for Ruby to allow non-whitelisted attributes to be used on a whitelisted HTML element.
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Analysis
by VulDB Data Team • 02/24/2023
The vulnerability identified as CVE-2018-3740 affects the Sanitize gem for Ruby, a widely used library designed to sanitize HTML content by removing potentially dangerous elements and attributes. This security flaw represents a critical bypass of the gem's intended protection mechanisms, allowing malicious actors to inject unauthorized HTML attributes even when the containing elements are properly whitelisted. The vulnerability stems from insufficient validation logic within the sanitization process that fails to properly enforce attribute restrictions on whitelisted HTML elements.
The technical implementation of this flaw involves the manipulation of HTML fragments through carefully crafted attribute structures that exploit gaps in the sanitization algorithm. When the Sanitize gem processes HTML content containing such malicious fragments, it incorrectly permits non-whitelisted attributes to persist on elements that are otherwise allowed in the whitelist. This occurs because the sanitization logic does not adequately distinguish between legitimate and malicious attribute usage patterns, particularly when dealing with nested or complex HTML structures that contain both whitelisted elements and unauthorized attributes. The vulnerability specifically targets the attribute filtering mechanism within the gem's processing pipeline, where the validation checks fail to comprehensively verify all attribute values against the configured whitelist policies.
The operational impact of CVE-2018-3740 extends beyond simple content injection, as it can enable sophisticated attack vectors including cross-site scripting attacks, malicious code execution, and potential privilege escalation within applications that rely on the Sanitize gem for HTML content processing. Attackers can leverage this vulnerability to bypass security controls implemented by web applications, potentially leading to data breaches, session hijacking, or unauthorized access to sensitive system resources. The vulnerability affects any Ruby application that utilizes the Sanitize gem for HTML sanitization, making it particularly concerning for web platforms, content management systems, and applications that process user-generated content. This flaw directly violates the principle of least privilege and can undermine the security posture of entire applications by allowing unauthorized attribute manipulation.
Security mitigations for this vulnerability require immediate patching of the Sanitize gem to version 4.6.4 or later, which contains the necessary fixes to properly validate attribute restrictions. Organizations should also implement additional defensive measures including comprehensive input validation, regular security scanning of dependencies, and monitoring for unauthorized attribute usage patterns. The vulnerability aligns with CWE-20, "Improper Input Validation," and can be categorized under ATT&CK technique T1210, "Exploitation of Remote Services," as it enables attackers to exploit weaknesses in web application security controls. System administrators should conduct thorough vulnerability assessments to identify applications using affected versions of the Sanitize gem and ensure proper patch management protocols are in place to prevent similar issues in other security libraries. Organizations should also consider implementing web application firewalls and additional content filtering mechanisms as defense-in-depth strategies to mitigate potential exploitation of this vulnerability.