Your squash plant probably does have the CMV virus if leaves are mottled, pale in parts, perhaps a little blistered or stunted. Not worth keeping the plant, I would compost it as I don’t think the virus persists in soil, being brought to plant leaves by aphids mostly, or via unhealthy seed, probably the case for your plant – are the others healthy?
Cucumber mosaic virus is common to other vegetables besides all cucurbits, including lettuce and spinach, also to groundsel and chickweed. I have noticed it sometimes but it rarely spreads to become a major problem here. Viruses are tricky, with no remedy once plants are infected and then you think "maybe they all will succumb’, but fortunately not, especially when… soil is healthy. I have a friend who is RHS judge and whenever looking around my gardens she comments on all the diseases, most of which I have not noticed, and she seems to ignore the good bits. My idea is to be mildly aware of disease and to work keenly for health.