CVE-2022-23517 in rails-html-sanitizer
Summary
by MITRE • 12/14/2022
rails-html-sanitizer is responsible for sanitizing HTML fragments in Rails applications. Certain configurations of rails-html-sanitizer < 1.4.4 use an inefficient regular expression that is susceptible to excessive backtracking when attempting to sanitize certain SVG attributes. This may lead to a denial of service through CPU resource consumption. This issue has been patched in version 1.4.4.
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Analysis
by VulDB Data Team • 11/05/2025
The rails-html-sanitizer gem serves as a critical security component within ruby on rails applications, specifically designed to sanitize HTML fragments and prevent cross-site scripting attacks by removing potentially dangerous elements and attributes. This vulnerability affects versions prior to 1.4.4 where the sanitization process contains a flaw in how it handles certain SVG attributes through inefficient regular expression patterns. The issue manifests when the sanitization engine encounters specific SVG attribute configurations that trigger excessive backtracking in the regular expression engine, causing the system to consume disproportionate CPU resources during the sanitization process. This particular weakness represents a classic denial of service vulnerability that can be exploited by malicious actors to disrupt service availability.
The technical flaw stems from the use of inefficient regular expressions within the sanitization logic that process SVG attributes containing specific patterns. When these patterns are processed, the regular expression engine enters into a state of excessive backtracking where it repeatedly revisits the same input positions, exponentially increasing processing time. This behavior is particularly problematic in SVG contexts where attribute values can contain complex nested structures that trigger the backtracking behavior. The vulnerability is classified under common weakness enumeration CWE-1321 which specifically addresses inefficient regular expressions that can lead to denial of service through resource exhaustion. The pattern matching complexity becomes exponential with input size, making even moderately sized SVG fragments capable of triggering the denial of service condition.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect application availability and system performance across entire rails deployments. When exploited, the vulnerability allows attackers to consume excessive CPU cycles through carefully crafted SVG content that triggers the inefficient regular expression patterns during sanitization. This can lead to complete service unavailability as the system becomes unresponsive to legitimate requests while processing the malicious input. The vulnerability affects all rails applications that utilize the affected version of rails-html-sanitizer for HTML sanitization, particularly those that accept user-generated content or process external HTML fragments containing SVG elements. The attack surface is broad since SVG content is commonly used in web applications for graphics, icons, and complex visual elements, making this a widespread concern for web application security.
Mitigation strategies should prioritize immediate patching to version 1.4.4 or later, which contains the fixed regular expression patterns that eliminate the excessive backtracking behavior. Organizations should conduct thorough testing of their applications after applying the patch to ensure no regression in functionality or sanitization behavior. Additional defensive measures include implementing input validation and sanitization at multiple layers, monitoring for unusual CPU consumption patterns, and establishing rate limiting mechanisms for HTML processing operations. The vulnerability demonstrates the importance of regular security audits and keeping dependencies updated, as this issue could have been prevented through proper version management and security scanning processes. From an attack detection perspective, security teams should monitor for unusual processing times during HTML sanitization operations and implement automated alerts for resource consumption anomalies. The fix addresses the core issue by optimizing the regular expression patterns to prevent backtracking while maintaining the same sanitization functionality, aligning with security best practices for preventing denial of service attacks through input processing.