Also, while sandboxing may be designed to prevent this, Messages is probably also designed not to crash on link sharing.
(Or am I wrong? I'm not a professional programmer. I'm just reasoning from common sense.)
If program gives up and exits on receipt of unexpected input, that can be perceived as a "crash" by the user but it's not exploitable.
If it's crashing because execution suddenly jumped somewhere it shouldn't be, and the OS killed it, that's more worriesome.