Debian: DLA-1466-1 Critical Denial Of Service Security Advisory

Juha-Matti Tilli discovered that a remote attacker can trigger the
worst case code paths for TCP stream reassembly with low rates of
specially crafted packets, leading to remote denial of service.

CVE-2018-5391 (FragmentSmack)

Juha-Matti Tilli discovered a flaw in the way the Linux kernel
handled reassembly of fragmented IPv4 and IPv6 packets. A remote
attacker can take advantage of this flaw to trigger time and
calculation expensive fragment reassembly algorithms by sending
specially crafted packets, leading to remote denial of service.

This is mitigated by reducing the default limits on memory usage
for incomplete fragmented packets. The same mitigation can be
achieved without the need to reboot, by setting the sysctls:

net.ipv4.ipfrag_high_thresh = 262144
net.ipv6.ip6frag_high_thresh = 262144
net.ipv4.ipfrag_low_thresh = 196608
net.ipv6.ip6frag_low_thresh = 196608

The default values may still be increased by local configuration