[phba]

Apparently X11 has a security extension [1]. There was a discussion some months ago [2].

Xenocara (X on OpenBSD) improves security by dropping privileges and using features like pledge [3], but I don't know how this affects the feasability of keyloggers.

[1] https://www.x.org/releases/X11R7.6/doc/xextproto/security.ht...

[2] https://news.ycombinator.com/item?id=44768745

[3] https://man.openbsd.org/pledge.2