I think there's a lot of people here making the wrong assumption about how their CFO would react to being told no.

These people aren't stupid. I'd expect them to understand risk better than your average senior software engineer and if you tell them "Sorry boss, too risky to do that right now. I can't be 100% sure this message is genuine. Let's sync on this after your meeting", your chances of promotion at this company would likely rise, not fall.