USN-3836-1: Linux kernel vulnerabilities

Releases

• Ubuntu 18.04 ESM

Packages

• linux - Linux kernel
• linux-gcp - Linux kernel for Google Cloud Platform (GCP) systems
• linux-kvm - Linux kernel for cloud environments
• linux-raspi2 - Linux kernel for Raspberry Pi 2

Details

Jann Horn discovered that the Linux kernel mishandles mapping UID or GID
ranges inside nested user namespaces in some situations. A local attacker
could use this to bypass access controls on resources outside the
namespace. (CVE-2018-18955)

Philipp Wendler discovered that the overlayfs implementation in the Linux
kernel did not properly verify the directory contents permissions from
within a unprivileged user namespace. A local attacker could use this to
expose sensitive information (protected file names). (CVE-2018-6559)

Update instructions

The problem can be corrected by updating your system to the following package versions:

Ubuntu 18.04

• linux-image-4.15.0-1027-kvm - 4.15.0-1027.27
• linux-image-4.15.0-1029-raspi2 - 4.15.0-1029.31
• linux-image-4.15.0-42-generic - 4.15.0-42.45
• linux-image-4.15.0-42-generic-lpae - 4.15.0-42.45
• linux-image-4.15.0-42-lowlatency - 4.15.0-42.45
• linux-image-4.15.0-42-snapdragon - 4.15.0-42.45

After a standard system update you need to reboot your computer to make
all the necessary changes.

ATTENTION: Due to an unavoidable ABI change the kernel updates have
been given a new version number, which requires you to recompile and
reinstall all third party kernel modules you might have installed.
Unless you manually uninstalled the standard kernel metapackages
(e.g. linux-generic, linux-generic-lts-RELEASE, linux-virtual,
linux-powerpc), a standard system upgrade will automatically perform
this as well.

References

• CVE-2018-18955
• CVE-2018-6559

Related notices

• USN-3835-1
• USN-3833-1
• USN-3836-2
• USN-3832-1