Nokogiri: Possible Out-of-Bounds Read in `Nokogiri::XML::NodeSet#[]`

Summary

### Summary `Nokogiri::XML::NodeSet#[]` (and its alias `#slice`) checked the requested index against the node set's bounds using a 32-bit-truncated copy of the index. A large negative index could pass the check and then be used at full width, reading outside the node set's storage. On CRuby this is an out-of-bounds read that typically crashes the process; on JRuby it is not memory-unsafe but returns an incorrect node. Nokogiri 1.19.4 performs the bounds check against the full-width index. ### Severity The Nokogiri maintainers have evaluated this as medium severity. Exploitation requires an application to pass an attacker-controlled integer to `NodeSet#[]`. The primary impact is a controlled crash (denial of service), with potential for memory disclosure on CRuby. On JRuby, Nokogiri is not affected by this vulnerability. ### Mitigation Upgrade to Nokogiri 1.19.4 or later. As a workaround, applications that index a `NodeSet` with externally-supplied integers can validate the index against `node_set.length` before use, or avoid passing untrusted values as an index. ### Credit This issue was responsibly reported by Zheng Yu from depthfirst.com.