Restlet Framework 2.1.x before 2.1.7 and 2.x.x before 2.2 RC1, when using XMLRepresentation or XML serializers, allows attackers to cause a denial of service via an XML Entity Expansion (XEE) attack.
https://github.com/advisories/GHSA-73cq-fhp3-8rpw
https://github.com/restlet/restlet-framework-java/wiki/XEE-security-enhancements
https://exchange.xforce.ibmcloud.com/vulnerabilities/91181