An issue was discovered in zsh before 5.6. The beginning of a #! script file was mishandled, potentially leading to an execve call to a program named on the second line.
https://www.zsh.org/mla/zsh-announce/136
https://usn.ubuntu.com/3764-1/
https://sourceforge.net/p/zsh/code/ci/1c4c7b6a4d17294df028322b70c53803a402233d
https://security.gentoo.org/glsa/201903-02
https://lists.debian.org/debian-lts-announce/2020/12/msg00000.html