mount.ecryptfs_private.c in eCryptfs-utils does not validate mount destination filesystem types, which allows local users to gain privileges by mounting over a nonstandard filesystem, as demonstrated by /proc/$pid.
Exploitability
AV:LAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:H8.4/CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H