Of course the ESS ExpressVote voting computer will have lots of security vulnerabilities. It's a computer, and computers have lots of vulnerabilities. This particular vulnerability is particularly interesting because it's the result of a security mistake in the design process. Someone didn't think the security through, and the result is a voter-verifiable paper audit trail that doesn't provide the security it promises.
Here are the details:
Now there's an even worse option than "DRE with paper trail"; I call it "press this button if it's OK for the machine to cheat" option. The country's biggest vendor of voting machines, ES&S, has a line of voting machines called ExpressVote. Some of these are optical scanners (which are fine), and others are "combination" machines, basically a ballot-marking device and an optical scanner all rolled into one.
This video shows a demonstration of ExpressVote all-in-one touchscreens purchased by Johnson County, Kansas. The voter brings a blank ballot to the machine, inserts it into a slot, chooses candidates. Then the machine prints those choices onto the blank ballot and spits it out for the voter to inspect. If the voter is satisfied, she inserts it back into the slot, where it is counted (and dropped into a sealed ballot box for possible recount or audit).
So far this seems OK, except that the process is a bit cumbersome and not completely intuitive (watch the video for yourself). It still suffers from the problems I describe above: voter may not carefully review all the choices, especially in down-ballot races; counties need to buy a lot more voting machines, because voters occupy the machine for a long time (in contrast to op-scan ballots, where they occupy a cheap cardboard privacy screen).
But here's the amazingly bad feature: "The version that we have has an option for both ways," [Johnson County Election Commissioner Ronnie] Metsker said. "We instruct the voters to print their ballots so that they can review their paper ballots, but they're not required to do so. If they want to press the button 'cast ballot,' it will cast the ballot, but if they do so they are doing so with full knowledge that they will not see their ballot card, it will instead be cast, scanned, tabulated and dropped in the secure ballot container at the backside of the machine." [TYT Investigates, article by Jennifer Cohn, September 6, 2018]
Now it's easy for a hacked machine to cheat undetectably! All the fraudulent vote-counting program has to do is wait until the voter chooses between "cast ballot without inspecting" and "inspect ballot before casting." If the latter, then don't cheat on this ballot. If the former, then change votes how it likes, and print those fraudulent votes on the paper ballot, knowing that the voter has already given up the right to look at it.
A voter-verifiable paper audit trail does not require every voter to verify the paper ballot. But it does require that every voter be able to verify the paper ballot. I am continuously amazed by how bad electronic voting machines are. Yes, they're computers. But they also seem to be designed by people who don't understand computer (or any) security.