Interact sure, but on election day no way would they be 'updating the firmware'. From my own personal experience there is always more than one person watching or hands-on the polling machines. I'm sure some places are probably more lax than my experience.

There is also variance in where you vote what machine they might have. My location has always been a scantron type and only one device per voting location. You'd have to know ahead of time what device is used where and have the correct exploit handy. Still in my scenario going to be hard to pull off an exploit while people are waiting to enter their ballots into the machine.

Not saying it couldn't be done but I'd say it is out there for a probable attack. They do make for good headlines and of course are something no one wants to see tampered with. I'm glad the one's in my district still have a paper trail, which has been used in the past to verify votes by hand when the election was close.