Frost Brand weapons have the following property, amongst others:
In freezing temperatures, the blade sheds bright light in a 10-foot radius and dim light for an additional 10 feet.
The other properties of Frost Brands directly benefit their attuned wearer (ability to extinguish flames by drawing the blade, fire resistance while holding it, extra cold damage while attacking with it), but the light-shedding property seems more of a passive thing (it would make sense, to me at least, that an unattuned, abandoned Frost Brand stuck in an Iceberg would glow).
The rules on attunement state the following:
Without becoming attuned to an item that requires attunement, a creature gains only its nonmagical benefits, unless its description states otherwise. For example, a magic Shield that requires attunement provides the benefits of a normal Shield to a creature not attuned to it, but none of its magical properties.
But this light shedding property does not seem to be intended to benefit its wearer in particular — seems more to be the blade’s natural reaction to extreme cold.
Considering that there are already attunement-based items with non-attunement properties (such as a Talisman of Pure Good’s contact damage to non-good creatures), does an unattuned Frostbrand still glow in freezing temperatures ?