Check and override options that could be potentially harmful to router
Although it is not likely it is possible to set log file and other options that could damage router. This is not about security but rather about destruction of device. In short there should be the only way how OpenVPN client could harm device and that is by writing too much to MMC.
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search openvpn documentation for options that can lead to writes to drive -
overwrite those options to sensible values (such as /dev/nullor/tmp/*)