A locking inconsistency issue was discovered in the tty subsystem of the Linux kernel through 5.9.13. drivers/tty/tty_io.c and drivers/tty/tty_jobctrl.c may allow a read-after-free attack against TIOCGSID, aka CID-c8bcd9c5be24.
https://www.debian.org/security/2021/dsa-4843
https://security.netapp.com/advisory/ntap-20210122-0001/
https://lists.debian.org/debian-lts-announce/2021/03/msg00010.html
https://lists.debian.org/debian-lts-announce/2021/02/msg00018.html