An issue was discovered on Fujitsu Wireless Keyboard Set LX390 GK381 devices. Because of the lack of proper encryption of 2.4 GHz communication, and because of password-based authentication, they are vulnerable to replay attacks.
packetstormsecurity.com/files/154954/Fujitsu-Wireless-Keyboard-Set-LX390-Replay-Attacks.html
www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2019-009.txt
www.syss.de/pentest-blog/2019/syss-2019-009-syss-2019-010-und-syss-2019-011-schwachstellen-in-weiterer-funktastatur-mit-sicherer-24-ghz-technologie/