However it takes quite a while until a new stable subrelease is prepared. Therefore the host security.debian.org has been set up as interim solution.
In order to keep your system stable all you need is to direct apt to
that host. Here are two configuration lines for
/etc/apt/sources.list, depending on your use of stable or
unstable.
deb http://security.debian.org/ stable updates deb http://security.debian.org/ unstable updates