The REXML gem before 3.3.9 has a ReDoS vulnerability when it parses an XML that has many digits between &# and x…; in a hex numeric character reference (&#x…;). This does not happen with Ruby 3.2 or later. Ruby 3.1 is the only affected maintained Ruby. Note that Ruby 3.1 will reach EOL on 2025-03.
The REXML gem before 3.3.6 has a DoS vulnerability when it parses an XML that has many deep elements that have same local name attributes. If you need to parse untrusted XMLs with tree parser API like REXML::Document.new, you may be impacted to this vulnerability. If you use other parser APIs such as stream parser API and SAX2 parser API, this vulnerability is not affected.
The REXML gem before 3.3.2 has a DoS vulnerability when it parses an XML that has many entity expansions with SAX2 or pull parser API. If you need to parse untrusted XMLs with SAX2 or pull parser API, you may be impacted to this vulnerability.
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 ]>. If you need to parse untrusted XMLs, you may be impacted to these vulnerabilities.
The REXML gem before 3.3.1 has some DoS vulnerabilities when it parses an XML that has many specific characters such as <, 0 and %>. If you need to parse untrusted XMLs, you may be impacted to these vulnerabilities.
The REXML gem before 3.2.6 has a DoS vulnerability when it parses an XML that has many <s in an attribute value. If you need to parse untrusted XMLs, you many be impacted to this vulnerability.
The REXML gem does not properly address XML round-trip issues. An incorrect document can be produced after parsing and serializing.