CVE-2022-23514: Loofah Library DoS Vulnerability

CVE-2022-23514 Overview

CVE-2022-23514 is a Regular Expression Denial of Service (ReDoS) vulnerability affecting Loofah, a widely-used Ruby library for manipulating and transforming HTML/XML documents and fragments built on top of Nokogiri. The vulnerability exists in versions prior to 2.19.1 and stems from an inefficient regular expression used when sanitizing certain SVG attributes. When processing specially crafted input, the vulnerable regex pattern is susceptible to excessive backtracking, leading to CPU resource exhaustion and potential denial of service conditions.

Critical Impact

Applications using vulnerable Loofah versions for HTML/SVG sanitization may be subject to denial of service attacks through CPU resource consumption when processing malicious SVG content.

Affected Products

• Loofah versions prior to 2.19.1
• Ruby applications using Loofah for HTML/XML sanitization
• Web applications leveraging Nokogiri-based document processing with Loofah

Discovery Timeline

• 2022-12-14 - CVE-2022-23514 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2022-23514

Vulnerability Analysis

This vulnerability falls under CWE-1333 (Inefficient Regular Expression Complexity), commonly known as ReDoS (Regular Expression Denial of Service). The flaw resides in Loofah's SVG attribute sanitization logic, where a poorly constructed regular expression pattern exhibits catastrophic backtracking behavior when confronted with adversarial input strings.

When Loofah processes HTML or XML documents containing SVG elements, it applies sanitization rules to filter potentially dangerous attributes. The vulnerable regular expression used in this process has exponential time complexity for certain input patterns. An attacker can exploit this by crafting SVG attributes that trigger worst-case regex evaluation, causing the Ruby process to consume excessive CPU cycles while attempting to match or reject the malicious input.

The vulnerability is particularly concerning for web applications that accept user-supplied HTML content and sanitize it before rendering or storage. Common use cases include content management systems, forum software, email clients with HTML rendering, and any application that processes untrusted HTML/SVG content.

Root Cause

The root cause is an inefficient regular expression pattern used during SVG attribute sanitization. The regex contains constructs that lead to excessive backtracking when the input string is crafted to exploit the pattern's structure. This is a classic algorithmic complexity vulnerability where the time required to evaluate the regex grows exponentially with input size, rather than linearly.

Regular expressions with nested quantifiers or overlapping alternatives are particularly susceptible to this class of vulnerability. When the regex engine attempts to match such patterns against non-matching input, it may explore an exponential number of possible matching paths before concluding that no match exists.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by submitting specially crafted SVG content to any application endpoint that processes user-supplied HTML/XML through Loofah's sanitization functions.

The attack is executed by including SVG elements with maliciously crafted attribute values designed to trigger catastrophic regex backtracking. When the application attempts to sanitize this content, the vulnerable regex pattern enters an extended processing state, consuming CPU resources and potentially rendering the application unresponsive. Additional details about the vulnerability can be found in the GitHub Security Advisory and the original HackerOne Report #1684163.

Detection Methods for CVE-2022-23514

Indicators of Compromise

• Abnormally high CPU utilization during HTML/XML processing operations
• Application request timeouts coinciding with HTML sanitization operations
• Increased response latency for endpoints handling user-submitted HTML content
• Ruby process hangs or unresponsiveness during content processing

Detection Strategies

• Monitor application performance metrics for unusual CPU spikes during content processing
• Implement request timeout monitoring for HTML sanitization endpoints
• Use dependency scanning tools to identify Loofah versions below 2.19.1
• Review application logs for timeout errors related to content sanitization operations

Monitoring Recommendations

• Configure alerting for sustained high CPU utilization on application servers
• Implement request duration monitoring with thresholds for sanitization endpoints
• Deploy runtime application self-protection (RASP) solutions to detect ReDoS patterns
• Use SentinelOne Singularity to monitor for anomalous process behavior and resource exhaustion patterns

How to Mitigate CVE-2022-23514

Immediate Actions Required

• Upgrade Loofah to version 2.19.1 or later immediately
• Audit all Ruby applications for Loofah dependency usage
• Implement request timeouts on endpoints processing user-supplied HTML content
• Consider input size limits for HTML content submitted to sanitization functions

Patch Information

The vulnerability has been addressed in Loofah version 2.19.1. The fix involves replacing the inefficient regular expression with an optimized pattern that does not exhibit catastrophic backtracking behavior. Organizations should update their Gemfile to specify the patched version and run bundle update loofah to apply the fix.

For Debian-based systems, security updates have been released as documented in the Debian LTS Security Announcements.

Workarounds

• Implement request timeout limits to prevent long-running sanitization operations from consuming resources indefinitely
• Apply input size restrictions on SVG content to reduce the effectiveness of ReDoS payloads
• Consider pre-filtering SVG elements from untrusted input if SVG functionality is not required
• Deploy rate limiting on endpoints that process user-supplied HTML content

# Update Loofah to patched version
bundle update loofah

# Verify installed version
bundle show loofah
# Should show loofah-2.19.1 or later

# Alternative: Specify minimum version in Gemfile
echo "gem 'loofah', '>= 2.19.1'" >> Gemfile
bundle install