In kdeconnect-kde (aka KDE Connect) before 20.08.2, an attacker on the local network could send crafted packets that trigger use of large amounts of CPU, memory, or network connection slots, aka a Denial of Service attack.
libdiscover/backends/KNSBackend/KNSResource.cpp in KDE Discover before 5.21.3 automatically creates links to potentially dangerous URLs (that are neither https:// nor http://) based on the content of the store.kde.org web site. (5.18.7 is also a fixed version.)