I'm not sure it's a new bug, just that if you look up that call you'll find if it's used with any path containing a "/", then it can be raced to check somewhere other that the place the original author intended.

That's why symlinks MUST die.

I think it's just that they're tricky when it comes to ownership. People who write code that depends on some type of file or directory ownership for security often don't think about the ways symlinks can be used to bypass their security model.

You can sort of think of a symlink as having 2 owners: the user that owns the symlink itself, and the user who owns the file pointed to by the symlink. One of those owners might be an attacker, so every time you interact with a file, you have to think "this file might be half-owned by an attacker, and half-owned by a victim".

I'm going to be giving a talk at SambaXP this year (it's virtual, so you only need to register to attend) explaining why IMHO symlinks have utterly broken the POSIX filesystem API, making it impossible for application developers to write secure applications.

https://sambaxp.org/

It's not just a whine, I'm also going to make some suggestions for fixing it :-).

DOS? Non-NT Windows?

I think that was one of Plan9's selling points.