Eclipse Leshan is a device management server and client Java implementation. In affected versions DDFFileParser` and `DefaultDDFFileValidator` (and so `ObjectLoader`) are vulnerable to `XXE Attacks`. A DDF file is a LWM2M format used to store LWM2M object description. Leshan users are impacted only if they parse untrusted DDF files (e.g. if they let external users provide their own model), in that case they MUST upgrade to fixed version. If you parse only trusted DDF file and validate only with trusted xml schema, upgrading is not mandatory. This issue has been fixed in versions 1.5.0 and 2.0.0-M13. Users are advised to upgrade. There are no known workarounds for this vulnerability.