What keeps private keys on hardware wallets safe/inaccessible?

Everytime I update the ledger live app I get an uneasy feeling that one day when I go to plug my ledger in the new update will be able to extract the keys from the device. What type of security is used within hardware wallets to protect against this? I know that the keys never leave the device meaning the device it's connected to should never be able to see it but can that change? via /r/Bitcoin https://bit.ly/32tUr4b