The REXML gem before 3.2.5 in Ruby before 2.6.7, 2.7.x before 2.7.3, and 3.x before 3.0.1 does not properly address XML round-trip issues. An incorrect document can be produced after parsing and serializing.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-28965
• ruby/rexml@2fe62e2
• ruby/rexml@3c137eb
• ruby/rexml@6a250d2
• ruby/rexml@9b311e5
• ruby/rexml@a659c63
• ruby/rexml@f7bab89
• ruby/rexml@f9d88e4
• https://hackerone.com/reports/1104077
• https://rubygems.org/gems/rexml
• https://www.ruby-lang.org/en/news/2021/04/05/xml-round-trip-vulnerability-in-rexml-cve-2021-28965/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/WTVFTLFVCSUE5CXHINJEUCKSHU4SWDMT/
• https://security.netapp.com/advisory/ntap-20210528-0003/
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rexml/CVE-2021-28965.yml