Index: /trunk/src/VBox/Devices/Network/slirp/tcp_input.c
===================================================================
--- /trunk/src/VBox/Devices/Network/slirp/tcp_input.c	(revision 19898)
+++ /trunk/src/VBox/Devices/Network/slirp/tcp_input.c	(revision 19899)
@@ -297,4 +297,12 @@
         so->so_m = 0;
         ti = so->so_ti;
+		/* @todo (r -vvl) clarify why it might happens */
+		if (ti == NULL)
+		{
+			LogRel(("NAT: ti is null. can't do any reseting connection actions\n"));
+			/* mbuf should be cleared in sofree called from tcp_close */
+			tcp_close(pData, tp);
+			return;
+		}
         tiwin = ti->ti_win;
         tiflags = ti->ti_flags;