RunC allowed additional container processes via 'runc exec' to be ptraced by the pid 1 of the container. This allows the main processes of the container, if running as root, to gain access to file-descriptors of these new processes during the initialization and can lead to container escapes or modification of runC state before the process is fully placed inside the container.
Exploitability
AV:LAC:HPR:HUI:NScope
S:UImpact
C:HI:HA:H6.4/CVSS:3.0/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H