zsh through version 5.4.2 is vulnerable to a stack-based buffer overflow in the utils.c:checkmailpath function. A local attacker could exploit this to execute arbitrary code in the context of another user.
https://usn.ubuntu.com/3764-1/
https://sourceforge.net/p/zsh/code/ci/31f72205630687c1cef89347863aab355296a27f/
https://security.gentoo.org/glsa/201805-10
https://lists.debian.org/debian-lts-announce/2020/12/msg00000.html
https://bugzilla.redhat.com/show_bug.cgi?id=1563395