How safe are commercial airliners from gallium infiltration? I recently saw a video on gallium infiltration on YouTube.  Gallium is a metal with a melting point somewhere between standard room temperature and human body temperature, meaning if you pick up a block of it sitting on the table, it will melt in your hand.  If this melted metal comes into contact with solid aluminum, it will seep into it and alloy with it, decreasing the strength of the aluminum to somewhere around that of tissue paper.
When I saw this, I immediately had a horrifying thought: aren't airplanes made of aluminum?  And when I've flown in the past, I've seen a few places where there's exposed metal.  This makes me wonder if a malicious person with no regards for their own safety wouldn't be able to bring down a plane with a novelty for children that anyone can buy for a few dollars.
If someone tried to do this, is there anything in the design of modern commercial airliners that would stop them?
Gallium does not interact strongly with steel so it is unlikely to damage hydraulic pipes (these are made from steel, not aluminium). Same source says it also does not interact much with polymers so unlikely to damage the insulated wiring or rubber hoses or epoxy floor panels. It may damage some sensitive point where important device is attached to the aluminium frame, but hopefully most of such places are not single points of failure.
All it can do is to make a hole in the fuselage under the very rare circumstances. Then the aircraft will be depressurized, descend and land. It is probably still not a good idea to allow gallium in the passenger compartment.