The following Linux kernel update has been released for Debian GNU/Linux 9

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Debian Security Advisory DSA-4272-1 security@debian.org
https://www.debian.org/security/ Salvatore Bonaccorso
August 14, 2018 https://www.debian.org/security/faq
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Package : linux
CVE ID : CVE-2018-5391

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
if necessary.

For the stable distribution (stretch), this problem has been fixed in
version 4.9.110-3+deb9u2.

We recommend that you upgrade your linux packages.

For the detailed security status of linux please refer to its security
tracker page at:
https://security-tracker.debian.org/tracker/linux

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://www.debian.org/security/

  Linux Security Update for Debian 9