kernel - What is the "Dirty COW" bug, and how can I secure my system against it? - Ask Ubuntu


i've heard of bug "dirty cow" allows user read access files write them , gain administrative access. how protect against bug?

the ancient dirty cow bug

this bug has been around since kernel version 2.6.22. allows local user read access gain administrative privileges. warning has been issued (softpedia: linux kernels 4.8.3, 4.7.9 & 4.4.26 lts out patch "dirty cow" security flaw) , users urged upgrade kernel linux kernel 4.8.3, linux kernel 4.7.9, , linux kernel 4.4.26 lts. this link misleading because these kernel versions not supported ubuntu.

this answer tailored ubuntu users , tells you:

  • recommended kernel versions ubuntu users
  • how display current kernel version
  • how apply fix ubuntu supported kernels
  • how apply fix non-supported ubuntu kernels

ubuntu users "dirty cow" recommended kernels

ubuntu released security updates on october 20, 2016 patch kernel used supported ubuntu versions: softpedia: canonical patches ancient "dirty cow" kernel bug in supported ubuntu oses

canonical urging users patch systems installing:

  • linux-image-4.8.0-26 (4.8.0-26.28) ubuntu 16.10
  • linux-image-4.4.0-45 (4.4.0-45.66) ubuntu 16.04 lts
  • linux-image-3.13.0-100 (3.13.0-100.147) ubuntu 14.04 lts
  • linux-image-3.2.0-113 (3.2.0-113.155) ubuntu 12.04 lts
  • linux-image-4.4.0-1029-raspi2 (4.4.0-1029.36)

the xenial hwe kernel ubuntu 14.04 lts updated well, version linux-image-4.4.0-45 (4.4.0-45.66~14.04.1), , trusty hwe kernel ubuntu 12.04 lts version linux-image-3.13.0-100 (3.13.0-100.147~precise1).

please update ubuntu installations following instructions provided canonical at: https://wiki.ubuntu.com/security/upgrades .

display current kernel version

to display current running kernel version open terminal ctrl+alt+t , type:

uname -a

the kernel version you booted with displayed this:

linux dell 4.8.1-040801-generic #201610071031 smp fri oct 7 14:34:10 utc 2016 x86_64 x86_64 x86_64 gnu/linux

remember after install new kernel patches, can still boot older kernel versions grub. older versions not have patch applied, case of kernel version 4.8.1.

once again remember kernel version 4.8.1 not supported ubuntu.

how fix ubuntu supported kernels

since ubuntu has released fix of bug, users need upgrade system. if daily security updates enabled kernel upgrade has been done. check kernel version list of kernels above.

if ubuntu has not automatically upgraded kernel version run:

sudo apt-get update sudo apt-get dist-upgrade sudo reboot

after rebooting check current kernel version repeating previous section instructions.

how fix non-supported ubuntu kernels

some installations newer hardware may using unsupported kernel such 4.8.1 or greater. if need manually upgrade kernel. although bug report link above says use kernel 4.8.3, of october 30, 2016, 4.8.5 recent , how install it:

cd /tmp wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.8.5/linux-headers-4.8.5-040805_4.8.5-040805.201610280434_all.deb wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.8.5/linux-headers-4.8.5-040805-generic_4.8.5-040805.201610280434_amd64.deb wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.8.5/linux-image-4.8.5-040805-generic_4.8.5-040805.201610280434_amd64.deb sudo dpkg -i *.deb sudo reboot

after rebooting check current kernel version repeating instructions 2 sections back.


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