http4s-scala-xml provides EntityDecoder[F, scala.xml.Elem] instances that parse XML message bodies. Prior to versions 0.24.1 and 1.0.0-M39, these decoders used a javax.xml.parsers.SAXParserFactory obtained from SAXParserFactory.newInstance without any security configuration. With the JDK's default settings, the parser resolves DOCTYPE declarations, external general and parameter entities, and external DTDs.An application that uses these decoders to parse untrusted XML is vulnerable to XML External Entity (XXE) attacks. An attacker can craft a request that discloses local files readable by the service process, performs server-side request forgery (SSRF) against internal network resources, and/or causes denial of service through entity expansion. Versions 0.24.1 and 1.0.0-M39 fix the issue.