GeoNetwork vulnerable to Remote Code Execution via unsafe Saxon XSLT processor configuration in formatter

GeoNetwork is a catalog application to manage spatially referenced resources. Prior to versions 4.4.12 and 4.2.17, the Saxon XSLT processor used to render formatters is configured without secure processing (`FEATURE_SECURE_PROCESSING`) and without disabling Java extension functions (`ALLOW_EXTERNAL_FUNCTIONS`). Any stylesheet loaded by GeoNetwork can therefore invoke
`java.lang.Runtime.exec()` or `java.lang.ProcessBuilder` directly, achieving arbitrary command execution as the GeoNetwork process user. A user with sufficient privileges to upload a formatter can deliver a `.xsl` file containing Java extension call that execute arbitrary OS commands with the privileges of the GeoNetwork process. The issue is patched in GeoNetwork versions 4.4.12 and 4.2.17.