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.
github.com/ruby/rexml
github.com/ruby/rexml/commit/2fe62e29094d95921d7e19abbd2e26b23d78dc5b
github.com/ruby/rexml/commit/3c137eb119550874b2b3e27d12b733ca67033377
github.com/ruby/rexml/commit/6a250d2cd1194c2be72becbdd9c3e770aa16e752
github.com/ruby/rexml/commit/9b311e59ae05749e082eb6bbefa1cb620d1a786e
github.com/ruby/rexml/commit/a659c63e37414506dfb0d4655e031bb7a2e73fc8
github.com/ruby/rexml/commit/f7bab8937513b1403cea5aff874cbf32fd5e8551
github.com/ruby/rexml/commit/f9d88e4948b4a43294c25dc0edb16815bd9d8618
github.com/rubysec/ruby-advisory-db/blob/master/gems/rexml/CVE-2021-28965.yml
hackerone.com/reports/1104077
lists.fedoraproject.org/archives/list/[email protected]/message/WTVFTLFVCSUE5CXHINJEUCKSHU4SWDMT
nvd.nist.gov/vuln/detail/CVE-2021-28965
rubygems.org/gems/rexml
security.netapp.com/advisory/ntap-20210528-0003
www.ruby-lang.org/en/news/2021/04/05/xml-round-trip-vulnerability-in-rexml-cve-2021-28965