The refrigerator has a sealed cooling system that is filled with a Freon refrigerant. If the refrigerator is still cooling, it is not likely that the Freon has leaked out. Even if it did, this Freon would not be toxic or harmful in the small amount contained in the refrigerator cooling system.
Spoiled foods can cause odors. After they are removed, the residue in the styrofoam insulation of the refrigerator can develop mold or mildew that can give off a gas-like smell.
Stagnant water and/or debris in the drain pan of the refrigerator could also be a source of the smell.
It is not likely that a dangerous or toxic gas is coming from the refrigerator even if it is the source of the bad smell as noted above.
A more dangerous situation could be caused by a gas appliance leak that may appear to be coming from the refrigerator. If you have gas appliances in your home and think that you have a gas leak, I recommend that you leave the home immediately and call the gas company from a neighbor's house. The gas company can check for a gas leak.