The authentication cookies are generated using an algorithm based on the username, hardcoded secret and the up-time, and can be guessed in a reasonable time.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:NA:N7.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NOther