Nokogiri: Possible Use-After-Free when setting an attribute value via `Nokogiri::XML::Attr#value=` or `#content=`

Summary

### Summary Nokogiri’s CRuby native extension could leave a Ruby wrapper pointing to freed memory when replacing the value of an XML attribute. If Ruby code had already accessed an attribute child node, `Nokogiri::XML::Attr#value=` could free the underlying native child node while the wrapper remained reachable through the document node cache. A later use of the freed child node or a Ruby GC mark could dereference an invalid pointer, causing an invalid read and a possible segfault. Nokogiri 1.19.4 preserves any already-wrapped attribute child nodes before replacing the attribute value. JRuby is not affected. ### Severity The Nokogiri maintainers have evaluated this as low severity. Reaching it requires an unusual API-usage pattern that does not arise during normal use. The application must directly access an attribute's child node and then replace that same attribute's value via `Attr#value=` or `#content=`. Nokogiri 1.19.4 makes this pattern safe with no change to the public API. Already-wrapped attribute child nodes are preserved before the value is replaced. ### Mitigation Upgrade to Nokogiri 1.19.4 or later. As a workaround, avoid accessing attribute child nodes directly via `Attr#child` or similar before mutating the same attribute’s value. ### Credit This issue was responsibly reported by Zheng Yu from depthfirst.com.