Debian Security Advisory

DLA-1466-1 linux-4.9 -- LTS security update

Date Reported:
15 Aug 2018
Affected Packages:
linux-4.9
Vulnerable:
Yes
Security database references:
In the Debian bugtracking system: Bug 893393, Bug 903122, Bug 903767, Bug 903776, Bug 903838, Bug 903914.
In Mitre's CVE dictionary: CVE-2018-5390, CVE-2018-5391, CVE-2018-13405.
More information:

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