Debian 9 Stretch DLA-2769-1 Critical: Libxstream-java Remote Code Exec

XStream itself sets up a whitelist by default now, i.e. it blocks all classes
except those types it has explicit converters for. It used to have a blacklist
by default, i.e. it tried to block all currently known critical classes of the
Java runtime. Main reason for the blacklist were compatibility, it allowed to
use newer versions of XStream as drop-in replacement. However, this approach
has failed. A growing list of security reports has proven, that a blacklist is
inherently unsafe, apart from the fact that types of 3rd libraries were not
even considered. A blacklist scenario should be avoided in general, because it
provides a false sense of security.

See also https://x-stream.github.io/security.html#framework

For Debian 9 stretch, these problems have been fixed in version
1.4.11.1-1+deb9u4.

We recommend that you upgrade your libxstream-java packages.

For the detailed security status of libxstream-java please refer to
its security tracker page at: