Campfire is a web-based chat application. In version 1.4.4 and earlier, when a Campfire message contains a link, the server fetches it to build an OpenGraph unfurl preview. "RestrictedHTTP::PrivateNetworkGuard" relied on Ruby's "IPAddr#private? `` IPAddr#loopback?", and "IPAddr#link_local?" predicates plus IPv4-mapped and IPv4-compatible checks, which do not cover several special-use ranges. An authenticated user can post a link to a hostname resolving to CGNAT "100.64.0.0/10", NAT64 "64:ff9b::/96" or "64:ff9b:1::/48", or 6to4 "2002::/16" to bypass the guard and cause server-side requests to internal network resources. The NAT64 and 6to4 ranges can embed an internal IPv4 target. Confidentiality impact is limited to returned OpenGraph metadata, and most internal endpoints return none. There is no integrity or availability impact. An initial fix was released in version 1.4.5.