Package        : linux-4.9
Version        : 4.9.110-3+deb9u2~deb8u1
CVE ID         : CVE-2018-5390 CVE-2018-5391 CVE-2018-13405
Debian Bug     : 893393 903122 903767 903776 903838 903914

Several vulnerabilities have been discovered in the Linux kernel that
may lead to a privilege escalation or denial of service.

CVE-2018-5390 (SegmentSmack)

    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
    if necessary.

CVE-2018-13405

    Jann Horn discovered that the inode_init_owner function in
    fs/inode.c in the Linux kernel allows local users to create files
    with an unintended group ownership allowing attackers to escalate
    privileges by making a plain file executable and SGID.

For Debian 8 "Jessie", these problems have been fixed in version
4.9.110-3+deb9u2~deb8u1. This update includes fixes for several
regressions in the latest point release.

The earlier version 4.9.110-3+deb9u1~deb8u1 included all the above
fixes except for CVE-2018-5391, which may be mitigated as explained
above.

We recommend that you upgrade your linux-4.9 packages.

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

-- 
Ben Hutchings - Debian developer, member of kernel, installer and LTS teams