This is exactly why I hate electronic voting. When I argue about it, people always tell me that it's easier to commit vote fraud with paper ballots.
Sure, it's easier for a single person to temper with a single paper ballot or even poll box, but it is much harder on a large scale. Tampering with every physical boxes and tallies in a country requires much more effort and organisation than exploiting a single vulnerability that applies to an endless series of identical machines.
Hmm... I'm trying to say in every election that was manipulated, it was not subtle fraud that was the problem. I have little doubt that some fraud happens. I just don't think it typically matters. In most cases where it was not detected, it had no bearing on the outcome.
Now, overt manipulation of the voting populace through propaganda or other means is very common and has definitely happened. Ballet fraud, though? Are there any documented cases of that being a thing that mattered?
Advances in mathematically verified software could help here - although mechanisms for verifying the manufacturing of chips all the way down the supply chain might be farther out.
Sure, it's easier for a single person to temper with a single paper ballot or even poll box, but it is much harder on a large scale. Tampering with every physical boxes and tallies in a country requires much more effort and organisation than exploiting a single vulnerability that applies to an endless series of identical machines.