CVE-2022-51000 in Nokogiri
Summary
by MITRE • 08/25/2026
Nokogiri before 1.13.2 (CRuby, when using packaged libraries) ships vendored libxml2 2.9.12 and libxslt 1.1.34, which are affected by two upstream CVEs. Via CVE-2021-30560 in libxslt, an application transforming XML with untrusted XSL stylesheets is vulnerable to a denial-of-service attack. Via CVE-2022-23308 in libxml2, an application parsing an untrusted document with parse option DTDVALID set to true and NOENT set to false may be vulnerable to denial of service, memory disclosure, or code execution. Nokogiri 1.13.2 upgrades vendored libxml2 to 2.9.13 and libxslt to 1.1.35.
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Analysis
by VulDB Data Team • 08/25/2026
The vulnerability in versions of the Nokogiri Ruby gem prior to release 1.13.2 stems from its reliance on outdated, vendored copies of the underlying C libraries libxml2 and libxslt. Specifically, these older releases bundle libxml2 version 2.9.12 and libxslt version 1.1.34. Because Nokogiri ships with these specific versions statically linked or bundled within its package to ensure consistent behavior across different operating systems, it inherits the security flaws present in those upstream libraries. This creates a significant risk for applications that utilize Nokogiri for processing XML data, particularly when handling input from untrusted sources such as user uploads or external API responses. The core issue is not necessarily a flaw in Nokogiri itself, but rather the inclusion of vulnerable third-party components that have known security defects which were subsequently patched by their respective maintainers.
One critical aspect of this vulnerability involves CVE-2021-30560 within libxslt. This specific defect allows for a denial-of-service attack when an application attempts to transform XML documents using XSL stylesheets provided by untrusted parties. If the stylesheet contains certain malformed or specifically crafted structures, it can cause the processing engine to enter an infinite loop or consume excessive resources, leading to service disruption. From a threat modeling perspective, this aligns with CWE-400, which describes Uncontrolled Resource Consumption, and is often associated with ATT&CK technique T1499, Endpoint Denial of Service. Attackers can exploit this by submitting malicious XSLT files that trigger the resource exhaustion condition, effectively taking down services that rely on XML transformation capabilities without requiring authentication or complex privilege escalation steps.
A more severe set of risks arises from CVE-2022-23308 within libxml2. This vulnerability affects applications that parse untrusted documents while having specific parsing options enabled: DTDVALID is set to true and NOENT is set to false. Under these conditions, the parser may be susceptible to denial-of-service attacks, memory disclosure vulnerabilities, or even arbitrary code execution. The mechanism typically involves improper handling of entity expansions or document type definitions that lead to buffer overflows or out-of-bounds reads. This scenario maps directly to CWE-120, Buffer Copy without Checking Size of Input, and potentially CWE-416, Use After Free, depending on the specific memory corruption vector exploited. The potential for code execution makes this particularly dangerous in server-side applications where Nokogiri is used to process sensitive data, as it could allow an attacker to gain control over the underlying system processes running the Ruby application.
The operational impact of these vulnerabilities extends beyond simple service interruption. In environments where XML parsing is part of a critical workflow, such as invoice processing, document management systems, or API gateways, exploiting CVE-2021-30560 can lead to significant downtime and loss of availability. Meanwhile, exploitation of CVE-2022-23308 poses a direct threat to data integrity and confidentiality through memory disclosure, potentially leaking sensitive information stored in the application's memory space. Furthermore, successful code execution via this flaw could result in full system compromise, allowing attackers to install backdoors, exfiltrate data, or pivot to other parts of the network. The severity is amplified by the fact that many developers may not be aware that Nokogiri bundles these libraries and thus might assume they are protected if their host system has newer versions installed, leading to a false sense of security.
To mitigate these risks, organizations must upgrade Nokogiri to version 1.13.2 or any later release. This update replaces the vulnerable vendored libxml2 with version 2.9.13 and libxslt with version 1.1.35, incorporating the upstream patches that resolve both CVE-2021-30560 and CVE-2022-23308. It is crucial to verify dependencies in Gemfile or similar configuration files to ensure this upgrade is applied consistently across all environments, including development, staging, and production. Additionally, developers should review their code for any usage of the DTDVALID and NOENT parsing options with untrusted input, as even patched versions benefit from defensive programming practices such as disabling unnecessary features like entity expansion when not required. Implementing strict input validation and using allowlists for XML structures can further reduce the attack surface. Regularly auditing third-party dependencies and keeping them updated is essential to maintaining a secure software supply chain in Ruby-based applications.