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.

Nokogiri versions before 1.19.4 contain a possible invalid (out-of-bounds) memory read in the protected internal Node#initialize_copy_with_args helper behind Node#dup and #clone, which unwrapped its source argument as an xmlNode without a type check. If application code calls this protected method with a non-Node argument (e.g., a Namespace), it reads an xmlNs out of bounds, crashing the process. This is only triggerable by a programming error and cannot be triggered by untrusted input or normal use of the public API. Only CRuby is affected. Version 1.19.4 adds a type check and raises TypeError.

Nokogiri before 1.18.3 contains a stack buffer overflow vulnerability in libxml2 when reporting DTD validation errors with long QName prefixes, and a use-after-free vulnerability during validation against untrusted XML Schemas. Attackers can trigger these vulnerabilities by providing malicious DTD content or untrusted XSD files to cause denial of service or potential code execution.

Nokogiri versions before 1.19.3 contain a memory leak in the XSLT Stylesheet transform method when processing Ruby strings containing null bytes. Attackers can exploit this by passing attacker-controlled input with null bytes to transform parameters, causing heap allocations to leak and enabling denial of service against long-running processes.

Nokogiri before 1.18.4 bundles a vulnerable version of libxslt (prior to 1.1.43) that contains two use-after-free vulnerabilities: CVE-2025-24855 (use-after-free of the XPath context node due to xsltEvalXPathStringNs leaking xpathCtxt->node) and CVE-2024-55549 (use-after-free related to excluded result prefixes/namespaces). Processing crafted XSLT can trigger memory corruption. Nokogiri 1.18.4 upgrades the bundled libxslt to 1.1.43 to resolve these issues.

Nokogiri versions before 1.19.3 contain regular expression denial of service vulnerabilities in the CSS selector tokenizer affecting string-literal and identifier tokenization. Attackers can inject adversarial CSS selectors into methods like Node#css, Node#at_css, and Searchable#search to cause exponential regex backtracking and denial of service.

Nokogiri versions before 1.19.1 fail to check the return value from xmlC14NExecute in the canonicalize method, returning an empty string on failure instead of raising an exception. Attackers can exploit this to bypass signature validation in downstream SAML libraries by providing invalid canonicalized XML that is incorrectly accepted as valid.

Nokogiri before 1.15.6 and 1.16.x before 1.16.2 (CRuby, when using the packaged libxml2) is affected by a use-after-free vulnerability in libxml2 (CVE-2024-25062) in the xmlTextReader module, which underlies Nokogiri::XML::Reader. When using the XML Reader interface with DTD validation and XInclude expansion enabled, processing a crafted XML document can lead to an xmlValidatePopElement use-after-free. Nokogiri 1.15.6 and 1.16.2 resolve this by upgrading the packaged libxml2 to 2.11.7 and 2.12.5 respectively. JRuby and installations using system libxml2 are not affected.

Nokogiri versions before 1.16.5 bundle libxml2 2.12.6, which is affected by CVE-2024-34459 in libxml2's xmllint tool. Nokogiri 1.16.5 upgrades the bundled libxml2 to 2.12.7 to address this. Per the maintainers, there is no impact to Nokogiri users because Nokogiri does not provide or expose the xmllint tool where the issue occurs.

Nokogiri before 1.18.8 packages a vulnerable version of libxml2 (before 2.13.8) that contains a heap-based buffer under-read (CVE-2025-32415) in the xmlSchemaIDCFillNodeTables function in xmlschemas.c. The issue can be triggered when validating against an untrusted XML Schema, or when validating untrusted documents against trusted schemas that use xsd:keyref in combination with recursively defined types that have additional identity constraints. Upstream and MITRE rate this issue as low severity.