VyOS (1.2.x) provides a TFTP Server functionality.
create an folder for the data to use it in the TFTP Server config
set service tftp-server directory /config/user-data/tftpdata/
set the listen-address in IPv4 or/and IPv6
set service tftp-server listen-address 10.10.1.254
set chance the default udp Port
set service tftp-server port 6969
to allow anonymous uploads
set service tftp-server allow-upload
Choose your directory location carefully or you will loose the content on image upgrades.
Any directory under /config is save at this will be migrated.