CVE-2022-23514 in Loofah
Summary
by MITRE • 12/14/2022
Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Loofah < 2.19.1 contains 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 is patched in version 2.19.1.
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Analysis
by VulDB Data Team • 11/05/2025
The vulnerability identified as CVE-2022-23514 affects Loofah, a Ruby library designed for HTML and XML document manipulation that operates on top of the Nokogiri gem. This library serves as a fundamental component in many web applications for sanitizing and processing structured documents, making its security implications particularly significant. The flaw manifests in the library's handling of SVG attribute sanitization, where it employs regular expressions that are susceptible to catastrophic backtracking behavior. This vulnerability specifically impacts versions prior to 2.19.1, with the issue being resolved through a patched release that addresses the underlying regex implementation.
The technical root cause of this vulnerability lies in the inefficient regular expression pattern used during SVG attribute sanitization processes. When processing certain malformed or specially crafted SVG content, the regular expression engine enters into a state of excessive backtracking where it repeatedly tries different combinations of pattern matching, leading to exponential time complexity. This behavior is classified as a classic example of regular expression denial of service or ReDoS vulnerability, which is catalogued under CWE-1321. The vulnerability occurs because the regex pattern lacks proper quantifier anchoring and fails to account for the potential for nested or recursive matching patterns that can cause the engine to consume CPU resources exponentially rather than linearly.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it represents a critical denial of service threat that can be exploited by malicious actors to disrupt web services. Attackers can craft specific SVG content that triggers the vulnerable regex pattern, causing the application to consume excessive CPU cycles and potentially leading to service unavailability for legitimate users. This vulnerability is particularly concerning in web applications that process user-uploaded content or accept SVG data from external sources, as it can be leveraged to perform resource exhaustion attacks without requiring authentication or special privileges. The attack vector aligns with ATT&CK technique T1499.004, which involves resource exhaustion through manipulation of input data, and demonstrates how seemingly benign document processing operations can become attack surfaces.
Mitigation strategies for CVE-2022-23514 primarily involve upgrading to Loofah version 2.19.1 or later, which contains the patched regex implementation that eliminates the excessive backtracking behavior. Organizations should also implement additional defensive measures such as input validation and sanitization at multiple layers of their application architecture. Regular security assessments and dependency monitoring should be maintained to identify and remediate similar vulnerabilities in other libraries and components. The fix implemented in version 2.19.1 demonstrates proper regex design principles including the use of possessive quantifiers and avoiding nested quantifiers that can lead to catastrophic backtracking, aligning with security best practices for regular expression usage in security-sensitive applications.