REXML is an XML toolkit for Ruby. The REXML gem before 3.3.2 has some DoS vulnerabilities when it parses an XML that has many specific characters such as whitespace character, >] and ]>. The REXML gem 3.3.3 or later include the patches to fix these vulnerabilities.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:NA:L5.3/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LResource Management