Impact

The REXML gems from 3.3.3 to 3.4.1 have a DoS vulnerability when parsing XML containing multiple XML declarations. If you need to parse untrusted XMLs, you may be impacted to these vulnerabilities.

Patches

REXML gems 3.4.2 or later include the patches to fix these vulnerabilities.

Workarounds

Don't parse untrusted XMLs.

References

https://www.ruby-lang.org/en/news/2025/09/18/dos-rexml-cve-2025-58767/ : An announcement on www.ruby-lang.org

REXML is an XML toolkit for Ruby. 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 3.3.6 or later include the patch to fix the vulnerability.

REXML is an XML toolkit for Ruby. The REXML gem 3.3.2 has a DoS vulnerability when it parses an XML that has many entity expansions with SAX2 or pull parser API. The REXML gem 3.3.3 or later include the patch to fix the vulnerability.

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.