emacsclient-mail.desktop in Emacs 28.1 through 28.2 is vulnerable to shell command injections through a crafted mailto: URI. This is related to lack of compliance with the Desktop Entry Specification. It is fixed in 29.0.90
https://www.openwall.com/lists/oss-security/2023/03/08/2
https://www.gabriel.urdhr.fr/2023/06/08/emacsclient-mail-shell-elisp-injections/
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=60204