Improper Restriction of XML External Entity Reference
In JetBrains Ktor versions prior to 2.3.5 default configuration of ContentNegotiation with XML format was vulnerable to XXE.
CWE-611 - Improper Restriction of XML External Entity Reference
Listed 4th in the 'OWASP Top Ten', XML External Entities (XXE) vulnerability allows attackers to provide an XML input that contains an external entity. When the XML is parsed, it can cause data extraction and manipulation, execution of commands, denial-of-service attacks, and server-side request forgery.