Vulnerability CVE-2017-8921

In FlightGear before 2017.2.1, the FGCommand interface allows overwriting any file the user has write access to, but not with arbitrary data: only with the contents of a FlightGear flightplan (XML). A resource such as a malicious third-party aircraft could exploit this to damage files belonging to the user. Both this issue and CVE-2016-9956 are directory traversal vulnerabilities in Autopilot/route_mgr.cxx - this one exists because of an incomplete fix for CVE-2016-9956.