libgd2 security update

Package        : libgd2
CVE ID         : CVE-2017-6362

A double-free vulnerability was discovered in the gdImagePngPtr()
function in libgd2, a library for programmatic graphics creation and
manipulation, which may result in denial of service or potentially the
execution of arbitrary code if a specially crafted file is processed.

For the oldstable distribution (jessie), this problem has been fixed
in version 2.1.0-5+deb8u11.

For the stable distribution (stretch), this problem has been fixed in
version 2.2.4-2+deb9u2.

For the unstable distribution (sid), this problem has been fixed in
version 2.2.5-1.

We recommend that you upgrade your libgd2 packages.

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://www.debian.org/security/