As SmokeDispenser says, it depends on exactly which distribution you're using. In most cases you'd be better off upgrading to a supported release...
You can always try adding the Debian security updates to your
apt setup, they probably won't break anything. First you need to determine which version of Debian your distribution is based on; then
if it's based on Debian 7 (Wheezy), use Wheezy LTS (only on
echo deb http://security.debian.org/ wheezy/updates main | sudo tee /etc/apt/sources.list.d/wheezy-security.list
if it's based on Debian 8 (Jessie), use the standard security updates:
echo deb http://security.debian.org jessie/updates main | sudo tee /etc/apt/sources.list.d/jessie-security.list
If it's older than that, you won't get any support from Debian either.
Depending on how your distribution builds upon Debian, you may need to add the standard (non-security) Debian repositories as well; either
echo deb http://httpredir.debian.org/debian/ wheezy main | sudo tee /etc/apt/sources.list.d/wheezy.list
for Debian 7, or
echo deb http://httpredir.debian.org/debian/ jessie main | sudo tee /etc/apt/sources.list.d/jessie.list
for Debian 8.