The flow_dissector feature in the Linux kernel 4.3 through 5.x before 5.3.10 has a device tracking vulnerability, aka CID-55667441c84f. This occurs because the auto flowlabel of a UDP IPv6 packet relies on a 32-bit hashrnd value as a secret, and because jhash (instead of siphash) is used. The hashrnd value remains the same starting from boot time, and can be inferred by an attacker. This affects net/core/flow_dissector.c and related code.
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.3.10
https://lists.debian.org/debian-lts-announce/2020/03/msg00001.html