Before WordPress 4.9.5, the URL validator assumed URLs with the hostname localhost were on the same host as the WordPress server.
{
"availability": "No subscription required",
"binaries": [
{
"binary_version": "4.9.5+dfsg1-1",
"binary_name": "wordpress"
},
{
"binary_version": "4.9.5+dfsg1-1",
"binary_name": "wordpress-l10n"
},
{
"binary_version": "4.9.5+dfsg1-1",
"binary_name": "wordpress-theme-twentyfifteen"
},
{
"binary_version": "4.9.5+dfsg1-1",
"binary_name": "wordpress-theme-twentyseventeen"
},
{
"binary_version": "4.9.5+dfsg1-1",
"binary_name": "wordpress-theme-twentysixteen"
}
]
}