diff --git a/hscontrol/state/auth_tagged_expiry_test.go b/hscontrol/state/auth_tagged_expiry_test.go
index c626fb009..4fa33cfd3 100644
--- a/hscontrol/state/auth_tagged_expiry_test.go
+++ b/hscontrol/state/auth_tagged_expiry_test.go
@@ -2201,3 +2201,52 @@ func TestPAKReregisterConcurrentAdminExpire(t *testing.T) {
 		require.True(t, n.IsExpired(), "iteration %d: the spent key revived an expired node", i)
 	}
 }
+
+func TestPreAuthKeyRegistrationOwnsHostinfo(t *testing.T) {
+	for _, name := range []string{"new", "reregister", "preserve NetInfo"} {
+		t.Run(name, func(t *testing.T) {
+			s := newRetagTestState(t)
+			user := s.CreateUserForTest("hostinfo-user")
+			pak, err := s.CreatePreAuthKey(user.TypedID(), true, false, nil, nil)
+			require.NoError(t, err)
+
+			machineKey := key.NewMachine().Public()
+
+			regReq := tailcfg.RegisterRequest{
+				Auth:    &tailcfg.RegisterResponseAuth{AuthKey: pak.Key},
+				NodeKey: key.NewNode().Public(),
+				Hostinfo: &tailcfg.Hostinfo{
+					Hostname: "original",
+					Services: []tailcfg.Service{{Proto: "tcp", Port: 80}},
+					NetInfo:  &tailcfg.NetInfo{PreferredDERP: 1},
+				},
+			}
+			if name != "new" {
+				_, _, err = s.HandleNodeFromPreAuthKey(regReq, machineKey)
+				require.NoError(t, err)
+			}
+
+			if name == "preserve NetInfo" {
+				regReq.Hostinfo.NetInfo = nil
+			}
+
+			original := regReq.Hostinfo.Clone()
+			node, _, err := s.HandleNodeFromPreAuthKey(regReq, machineKey)
+			require.NoError(t, err)
+			require.Equal(t, original, regReq.Hostinfo, "registration must not modify its request")
+
+			regReq.Hostinfo.Hostname = "changed"
+
+			regReq.Hostinfo.Services[0].Port = 443
+			if regReq.Hostinfo.NetInfo != nil {
+				regReq.Hostinfo.NetInfo.PreferredDERP = 2
+			}
+
+			stored, ok := s.GetNodeByID(node.ID())
+			require.True(t, ok)
+			require.Equal(t, "original", stored.Hostinfo().Hostname())
+			require.Equal(t, uint16(80), stored.Hostinfo().Services().At(0).Port)
+			require.Equal(t, tailcfg.DERPRegionID(1), stored.Hostinfo().NetInfo().PreferredDERP())
+		})
+	}
+}
diff --git a/hscontrol/state/maprequest_test.go b/hscontrol/state/maprequest_test.go
index fe384abdb..f5ba839ce 100644
--- a/hscontrol/state/maprequest_test.go
+++ b/hscontrol/state/maprequest_test.go
@@ -21,6 +21,43 @@ import (
 	"tailscale.com/types/opt"
 )
 
+func TestMapRequestOwnsRequestData(t *testing.T) {
+	_, s, nodeID := persistTestSetup(t)
+	t.Cleanup(func() { _ = s.Close() })
+
+	node, ok := s.GetNodeByID(nodeID)
+	require.True(t, ok)
+
+	req := tailcfg.MapRequest{
+		NodeKey:   node.NodeKey(),
+		DiscoKey:  node.DiscoKey(),
+		Endpoints: []netip.AddrPort{netip.MustParseAddrPort("192.0.2.1:41641")},
+		Hostinfo: &tailcfg.Hostinfo{
+			Hostname: "original",
+			Services: []tailcfg.Service{{Proto: "tcp", Port: 80}},
+			NetInfo: &tailcfg.NetInfo{
+				PreferredDERP: 1,
+				DERPLatency:   map[string]float64{"1-v4": 0.1},
+			},
+		},
+	}
+	original := req.Hostinfo.Clone()
+	_, err := s.UpdateNodeFromMapRequest(nodeID, req)
+	require.NoError(t, err)
+	require.Equal(t, original, req.Hostinfo, "map update must not modify its request")
+
+	req.Hostinfo.Hostname = "changed"
+	req.Hostinfo.Services[0].Port = 443
+	req.Hostinfo.NetInfo.PreferredDERP = 2
+	req.Hostinfo.NetInfo.DERPLatency["1-v4"] = 0.2
+	req.Endpoints[0] = netip.MustParseAddrPort("192.0.2.2:41641")
+
+	stored, ok := s.GetNodeByID(nodeID)
+	require.True(t, ok)
+	require.Equal(t, original, stored.Hostinfo().AsStruct())
+	require.Equal(t, netip.MustParseAddrPort("192.0.2.1:41641"), stored.Endpoints().At(0))
+}
+
 func TestNetInfoFromMapRequest(t *testing.T) {
 	nodeID := types.NodeID(1)
 
diff --git a/hscontrol/state/state.go b/hscontrol/state/state.go
index 152ecf643..09f4fd51d 100644
--- a/hscontrol/state/state.go
+++ b/hscontrol/state/state.go
@@ -2776,8 +2776,7 @@ func (s *State) HandleNodeFromPreAuthKey(
 	}
 
 	// Ensure we have valid hostinfo
-	validHostinfo := cmp.Or(regReq.Hostinfo, &tailcfg.Hostinfo{})
-	validHostinfo.Hostname = hostname
+	validHostinfo := cmp.Or(regReq.Hostinfo.Clone(), &tailcfg.Hostinfo{})
 
 	log.Debug().
 		Caller().
@@ -3520,7 +3519,8 @@ func (s *State) UpdateNodeFromMapRequest(id types.NodeID, req tailcfg.MapRequest
 		currentNode.ApplyPeerChange(&delta.peerChange)
 
 		if hostinfoToStore {
-			currentNode.Hostinfo = newHostinfo
+			// The snapshot outlives the request; deep-copy so its slices and NetInfo are never shared.
+			currentNode.Hostinfo = newHostinfo.Clone()
 		}
 
 		// Only a real hostname change may re-derive GivenName: it is peer
diff --git a/hscontrol/types/node.go b/hscontrol/types/node.go
index 06d255ebe..e85f80b57 100644
--- a/hscontrol/types/node.go
+++ b/hscontrol/types/node.go
@@ -661,7 +661,7 @@ func (node *Node) PeerChangeFromMapRequest(req tailcfg.MapRequest) tailcfg.PeerC
 
 	// Compare endpoints using order-independent comparison
 	if EndpointsChanged(node.Endpoints, req.Endpoints) {
-		ret.Endpoints = req.Endpoints
+		ret.Endpoints = slices.Clone(req.Endpoints)
 	}
 
 	now := time.Now()