CVE-2022-23476 is a vulnerability found in Nokogiri, an open-source XML and HTML parsing library widely used in Ruby applications. Specifically, versions 1.13.8 and 1.13.9 of Nokogiri fail to properly check the return value of the function xmlTextReaderExpand within the method Nokogiri::XML::Reader#attribute_hash. This unchecked return value can lead to a null pointer dereference when the library attempts to parse malformed or invalid XML/HTML markup. The consequence of this flaw is that it may cause the application using Nokogiri to crash or terminate unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is particularly relevant for applications that utilize the XML::Reader interface to parse untrusted or user-supplied XML inputs, as attackers could craft malicious markup to trigger the null pointer exception. The root cause is a failure to handle error conditions correctly (CWE-252: Unchecked Return Value), which leads to a null pointer dereference (CWE-476). While no known exploits have been reported in the wild, the vulnerability is considered medium severity due to its potential to disrupt service availability. The recommended remediation is to upgrade Nokogiri to version 1.13.10 or later, where this issue has been addressed. Developers can audit their codebases for usage of XML::Reader#attributes or XML::Reader#attribute_hash methods to assess exposure to this vulnerability.

For European organizations, the primary impact of this vulnerability is the risk of denial of service attacks against applications that rely on Nokogiri for XML/HTML parsing, especially those processing untrusted inputs such as web services, APIs, or data ingestion pipelines. A successful exploitation could cause application crashes, leading to service interruptions, degraded user experience, and potential operational disruptions. While this vulnerability does not directly compromise confidentiality or integrity, the availability impact can be significant for critical systems. Organizations in sectors with high reliance on Ruby-based applications—such as financial services, e-commerce, and government digital services—may face increased risk. Additionally, denial of service conditions could be leveraged as part of multi-stage attacks or to distract security teams. Given the widespread use of Nokogiri in Ruby environments, the scope of affected systems can be broad, especially in organizations with legacy or unpatched software. The absence of known exploits reduces immediate risk but does not eliminate the threat, as attackers could develop exploits targeting this flaw.

1. Immediate upgrade of Nokogiri to version 1.13.10 or later is the most effective mitigation to eliminate the vulnerability. 2. Conduct a thorough code audit to identify all instances where XML::Reader#attributes or XML::Reader#attribute_hash are used, especially in contexts processing untrusted XML inputs. 3. Implement input validation and sanitization for XML data before parsing to reduce the risk of malformed markup triggering the vulnerability. 4. Employ runtime application monitoring to detect abnormal crashes or service interruptions that may indicate exploitation attempts. 5. For critical applications, consider adding fallback or error-handling mechanisms to gracefully handle parsing failures without crashing the entire service. 6. Maintain an up-to-date inventory of Ruby dependencies and integrate automated dependency scanning tools into the CI/CD pipeline to detect vulnerable versions proactively. 7. Educate development teams about secure XML parsing practices and the importance of handling return values and error conditions robustly.