FreeBSD-SA-19:11.cd_ioctl Security Advisory
The FreeBSD Project
Topic: Privilege escalation in cd(4) driver
Credits: Alex Fortune
Affects: All supported versions of FreeBSD.
Corrected: 2019-07-03 00:11:31 UTC (stable/12, 12.0-STABLE)
2019-07-02 00:03:55 UTC (releng/12.0, 12.0-RELEASE-p7)
2019-07-03 00:12:50 UTC (stable/11, 11.3-PRERELEASE)
2019-07-02 00:03:55 UTC (releng/11.3, 11.3-RC3-p1)
2019-07-02 00:03:55 UTC (releng/11.2, 11.2-RELEASE-p11)
CVE Name: CVE-2019-5602
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
The cd(4) driver implements a number of ioctls to permit low-level access to
the media in the CD-ROM device. The Linux emulation layer provides a
corresponding set of ioctls, some of which are implemented as wrappers of
native cd(4) ioctls.
These ioctls are available to users in the operator group, which gets
read-only access to cd(4) devices by default.
II. Problem Description
To implement one particular ioctl, the Linux emulation code used a special
interface present in the cd(4) driver which allows it to copy subchannel
information directly to a kernel address. This interface was erroneously
made accessible to userland, allowing users with read access to a cd(4)
device to arbitrarily overwrite kernel memory when some media is present in
A user in the operator group can make use of this interface to gain root
privileges on a system with a cd(4) device when some media is present in the
devfs.conf(5) and devfs.rules(5) can be used to remove read permissions from
Upgrade your vulnerable system to a supported FreeBSD stable or release /
security branch (releng) dated after the correction date.
Perform one of the following:
1) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
Afterwards, reboot the system.
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
On Tue, Jul 02, 2019 at 06:55:26PM -0700, Ronald F. Guilmette wrote:
> In message <[hidden email]>,
> [hidden email] wrote:
> >Topic: Privilege escalation in cd(4) driver
> >devfs.conf(5) and devfs.rules(5) can be used to remove read permissions from
> >cd(4) devices.
> Would it be accurate to say that another possible workaround would be to
> simply remove the optical drive from the system(s) entirely?
That's correct. Note though that the problem can only be triggered when
some media is present in the drive in the first place.