Note: this is the fourth version of this patch.

Apply by doing
	cd /usr/src/sys/netinet
	patch -p0 < rst.patch

And then rebuild your kernel.

Index: tcp_input.c
===================================================================
RCS file: /cvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.19
diff -u -r1.19 tcp_input.c
--- tcp_input.c	1998/06/27 02:42:40	1.19
+++ tcp_input.c	1999/02/19 06:24:46
@@ -1083,10 +1083,7 @@
 	 *	Close the tcb.
 	 */
 	if (tiflags & TH_RST) {
-
-		if ((ti->ti_seq != tp->rcv_nxt) &&
-		    (ti->ti_ack && ((SEQ_GT(ti->ti_ack, tp->snd_nxt) ||
-		      SEQ_LT(ti->ti_ack, (tp->snd_nxt - tp->snd_wnd))))))
+		if (ti->ti_seq != tp->last_ack_sent)
 			goto drop;
 
 		switch (tp->t_state) {
