Great example of out-of-bounds array/struct access being exploited for optimisation by gcc:
miniblog.
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An actively exploited security issue in keyfobs that work by proximity: malicious users can replay signals from the house to the car! https://geekologie.com/2019/08/gone-in-thirty-seconds-doorbell-cam-foot.php
Newer cars use rolling keycodes so you can't replay the same code after locking, but this seems harder to defend against.