Debian DSA-4272-1 : linux - security update
High Nessus Plugin ID 111707
SynopsisThe remote Debian host is missing a security-related update.
Description- 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_low_thresh = 196608 net.ipv6.ip6frag_low_thresh = 196608 net.ipv4.ipfrag_high_thresh = 262144 net.ipv6.ip6frag_high_thresh = 262144
The default values may still be increased by local configuration if necessary.
SolutionUpgrade the linux packages.
For the stable distribution (stretch), this problem has been fixed in version 4.9.110-3+deb9u2.