core: Allow loopback hosts for admin endpoint (fix #5650) (#5664)

1 files changed, 25 insertions, 0 deletions

diff --git a/admin.go b/admin.go
index 4a1d23b60..1966556a5 100644
--- a/admin.go
+++ b/admin.go
@@ -318,7 +318,32 @@ func (admin AdminConfig) allowedOrigins(addr NetworkAddress) []*url.URL {
 				// messages. If the requested URI does not include an Internet host
 				// name for the service being requested, then the Host header field MUST
 				// be given with an empty value."
+				//
+				// UPDATE July 2023: Go broke this by patching a minor security bug in 1.20.6.
+				// Understandable, but frustrating. See:
+				// https://github.com/golang/go/issues/60374
+				// See also the discussion here:
+				// https://github.com/golang/go/issues/61431
+				//
+				// We can no longer conform to RFC 2616 Section 14.26 from either Go or curl
+				// in purity. (Curl allowed no host between 7.40 and 7.50, but now requires a
+				// bogus host; see https://superuser.com/a/925610.) If we disable Host/Origin
+				// security checks, the infosec community assures me that it is secure to do
+				// so, because:
+				// 1) Browsers do not allow access to unix sockets
+				// 2) DNS is irrelevant to unix sockets
+				//
+				// I am not quite ready to trust either of those external factors, so instead
+				// of disabling Host/Origin checks, we now allow specific Host values when
+				// accessing the admin endpoint over unix sockets. I definitely don't trust
+				// DNS (e.g. I don't trust 'localhost' to always resolve to the local host),
+				// and IP shouldn't even be used, but if it is for some reason, I think we can
+				// at least be reasonably assured that 127.0.0.1 and ::1 route to the local
+				// machine, meaning that a hypothetical browser origin would have to be on the
+				// local machine as well.
 				uniqueOrigins[""] = struct{}{}
+				uniqueOrigins["127.0.0.1"] = struct{}{}
+				uniqueOrigins["::1"] = struct{}{}
 			} else {
 				uniqueOrigins[net.JoinHostPort("localhost", addr.port())] = struct{}{}
 				uniqueOrigins[net.JoinHostPort("::1", addr.port())] = struct{}{}