Is it danger to join cracked Minecraft server with Premium Account?

I haven't ever seen that people could steal anybody's account just because it used a license version

I'm not sure how usernames are set on cracked minecraft clients. But if you build something there, do not be surprised if someone comes on with your MC name and takes or griefs your stuff.

Find a regular server that verifies MC names with minecraft.net and hopefully has some means to protect your stuff or at least minimize griefers.

I don't know. I think you can join like trusted servers (big, long lasting cracked servers) Not like 24h or 1month servers! They could steal all that. I know my friend has made a server and asked for ppl on other servers to join it and they can see their passwords and then they go on that server and use that pass and they get their stuffs. (i don't know if i had bad grammar)