Adding following lines into the .ovpn file before I import it to Network Manager on Ubuntu fixed DNS leak with my VPN connection established by NetworkManager.
script-security 2 up /etc/openvpn/update-resolv-conf down /etc/openvpn/update-resolv-conf
These lines should be added below the lines of initial commands and before the lines of certificates.
Software developer. Defender of Kaer Morhen. Based in the U.S.
It is claimed that security is weakened by “script-security 2”. Please be prudent and do research before using this (and any) method.
BTW, I don’t have any DNS leak issue in default debian 9 & openvpn installation.