GHSA-v995-44v6-5fqm: JRuby: NONET is bypassed for external DTDs and entities when the systemId uses a short-form IPv4 host

Summary

On JRuby, the NONET parse option did not block an external DTD or entity whose system identifier used a short-form IPv4 host, such as http://127.1/ or http://169.254.43518/, or was an absolute path such as /x.dtd in a document parsed from a network URL. An application that parses untrusted XML with DTDLOAD, DTDVALID or NOENT could be made to send network requests, potentially enabling SSRF.

Nokogiri 1.19.5 applies the XML::Schema check from GHSA-8678-w3jw-xfc2: with NONET set, only local resources are loaded.

Only JRuby is affected. Default parse options are not affected.

Severity

The Nokogiri maintainers have evaluated this as low severity.

Mitigation

Upgrade to Nokogiri 1.19.5 or later, or do not enable DTDLOAD, DTDVALID or NOENT for untrusted input.

Credit

This issue was responsibly reported by @arpitjain099.