Mattermost versions 9.5.x <= 9.5.9 fail to properly filter the channel data when ElasticSearch is enabled which allows a user to get private channel names by using cmd+K/ctrl+K.
Exploitability
AV:NAC:LPR:LUI:NScope
S:UImpact
C:LI:NA:N4.3/CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:NConfiguration