Libguestfs - Jun 2018 - FYI: CVE-2018-11806 Qemu: slirp: heap buffer overflow while reassembling fragmented datagrams

There's a heap overflow in qemu SLIRP which affects libguestfs,
potentially allowing a malicious filesystem to take control of the
confining qemu process and from there attack the host.

It will affect libguestfs specifically when these two conditions are
both met:

 - You're using the ‘direct’ backend.

 - Networking is enabled.

The direct backend is the default upstream, but not in
Fedora/RHEL/CentOS.  It might also have been selected if you set the
LIBGUESTFS_BACKEND=direct environment variable or called
‘guestfs_set_backend (g, "direct")’.

Networking is enabled automatically by some tools (eg. virt-builder),
or is enabled if your code called ‘guestfs_set_network (g, 1)’ (which
is not the default).

Note that the libvirt backend is _not_ affected, for two reasons:
(1) It doesn't use SLIRP for networking (2) libvirt will use SELinux
to confine the qemu process, so even if the appliance gains full
control over qemu it is limited in what it can do.

The solution in any case is to upgrade to a qemu containing the fix.
Here's the upstream qemu patch:

  https://lists.gnu.org/archive/html/qemu-devel/2018-06/msg01012.html

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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