templates/forms/thanks.html in Formspree before 2018-01-23 allows XSS related to the _next parameter.
{
"unresolved_ranges": [
{
"cpes": [
"cpe:2.3:a:formspree:formspree:*:*:*:*:*:*:*:*"
],
"extracted_events": [
{
"fixed": "2018-01-23"
}
],
"source": "CPE_RANGE",
"vendor_product": "formspree:formspree"
},
{
"extracted_events": [
{
"fixed": "2018-01-23"
}
],
"source": "DESCRIPTION"
}
]
}