The HTTP Alternative Services header, Alt-Svc, can be used by a malicious site to scan all TCP ports of any host that the accessible to a user when web content is loaded. This vulnerability affects Firefox < 68.
6868Exploitability
AV:NAC:LPR:NUI:RScope
S:CImpact
C:LI:NA:N4.7/CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N