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.