My favourite unsafe one-liner:
eval((lambda:0).__code__.replace(co_consts=()))
This one is slightly cheat-y because it
does modify the code object, just not the bytecode itself.
"Purer" unsafety issues are treated as bugs and patched, but that doesn't stop them from existing periodically. I don't have a specific example on-hand but I bet you can find some in here: https://github.com/search?q=repo%3Apython%2Fcpython+segmenta...
Edit: This one is a decent example (and hasn't been fixed for a long time) https://github.com/python/cpython/issues/74957