Nextcloud Server is a Nextcloud package that handles data storage. In versions prior to 19.0.13, 20.011, and 21.0.3, there was a lack of ratelimiting on the shareinfo endpoint. This may have allowed an attacker to enumerate potentially valid share tokens. The issue was fixed in versions 19.0.13, 20.0.11, and 21.0.3. There are no known workarounds.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:LA:N5.3/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:NOther