profile.php in ExtCalendar 2 and earlier allows remote attackers to change the passwords of arbitrary users without providing the original password, and possibly perform other unauthorized actions, via modified values to register.php.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:H9.8/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H