textview_uri_security_check in textview.c in Claws Mail before 3.18.0, and Sylpheed through 3.7.0, does not have sufficient link checks before accepting a click. https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-37746 Патч есть в Fedora
В Сизифе claws-mail-3.18.0.