Patch by Stefan Tomanek <stefan@pico.ruhr.de> for dsniff >= 2.4b1 to add add -r
switch to poison both directions. For some more information, please have a look to
Debian bug ID #650749.

--- dsniff-2.4/arpspoof.8			2000-11-28 08:43:43.000000000 +0100
+++ dsniff-2.4/arpspoof.8.arpspoof_reverse	2013-12-20 20:27:49.000000000 +0100
@@ -9,7 +9,7 @@
 .na
 .nf
 .fi
-\fBarpspoof\fR [\fB-i \fIinterface\fR] [\fB-t \fItarget\fR] \fIhost\fR
+\fBarpspoof\fR [\fB\-i \fIinterface\fR] [\fB\-t \fItarget\fR] [\fB\-r\fR] \fIhost\fR
 .SH DESCRIPTION
 .ad
 .fi
@@ -26,6 +26,9 @@
 .IP "\fB-t \fItarget\fR"
 Specify a particular host to ARP poison (if not specified, all hosts
 on the LAN).
+.IP "\fB\-r\fR"
+Poison both hosts (host and target) to capture traffic in both directions.
+(only valid in conjuntion with \-t)
 .IP \fIhost\fR
 Specify the host you wish to intercept packets for (usually the local
 gateway).
--- dsniff-2.4/arpspoof.c			2013-12-20 20:25:04.000000000 +0100
+++ dsniff-2.4/arpspoof.c.arpspoof_reverse	2013-12-20 20:34:31.000000000 +0100
@@ -7,6 +7,8 @@
  * Copyright (c) 1999 Dug Song <dugsong@monkey.org>
  *
  * $Id: arpspoof.c,v 1.5 2001/03/15 08:32:58 dugsong Exp $
+ *
+ * Improved 2011 by Stefan Tomanek <stefa@pico.ruhr.de>
  */
 
 #include "config.h"
@@ -31,12 +33,13 @@
 static struct ether_addr spoof_mac, target_mac;
 static in_addr_t spoof_ip, target_ip;
 static char *intf;
+static int poison_reverse;
 
 static void
 usage(void)
 {
 	fprintf(stderr, "Version: " VERSION "\n"
-		"Usage: arpspoof [-i interface] [-t target] host\n");
+		"Usage: arpspoof [-i interface] [-t target] [-r] host\n");
 	exit(1);
 }
 
@@ -133,18 +136,30 @@
 static void
 cleanup(int sig)
 {
+	int fw = arp_find(spoof_ip, &spoof_mac);
+	int bw = poison_reverse && target_ip && arp_find(target_ip, &target_mac);
 	int i;
 	
-	if (arp_find(spoof_ip, &spoof_mac)) {
-		for (i = 0; i < 3; i++) {
-			/* XXX - on BSD, requires ETHERSPOOF kernel. */
+	fprintf(stderr, "Cleaning up and re-arping targets...\n");
+	for (i = 0; i < 5; i++) {
+		/* XXX - on BSD, requires ETHERSPOOF kernel. */
+		if (fw) {
 			arp_send(l, ARPOP_REPLY,
 				 (u_int8_t *)&spoof_mac, spoof_ip,
 				 (target_ip ? (u_int8_t *)&target_mac : NULL),
 				 target_ip);
+			/* we have to wait a moment before sending the next packet */
+			sleep(1);
+		}
+		if (bw) {
+			arp_send(l, ARPOP_REPLY,
+				 (u_int8_t *)&target_mac, target_ip,
+				 (u_int8_t *)&spoof_mac,
+				 spoof_ip);
 			sleep(1);
 		}
 	}
+	
 	exit(0);
 }
 
@@ -159,8 +174,9 @@
 	
 	intf = NULL;
 	spoof_ip = target_ip = 0;
+	poison_reverse = 0;
 	
-	while ((c = getopt(argc, argv, "i:t:h?V")) != -1) {
+	while ((c = getopt(argc, argv, "ri:t:h?V")) != -1) {
 		switch (c) {
 		case 'i':
 			intf = optarg;
@@ -169,6 +185,9 @@
 			if ((target_ip = libnet_name2addr4(l, optarg, LIBNET_RESOLVE)) == -1)
 				usage();
 			break;
+		case 'r':
+			poison_reverse = 1;
+			break;
 		default:
 			usage();
 		}
@@ -179,6 +198,11 @@
 	if (argc != 1)
 		usage();
 	
+	if (poison_reverse && !target_ip) {
+		errx(1, "Spoofing the reverse path (-r) is only available when specifying a target (-t).");
+		usage();
+	}
+	
 	if ((spoof_ip = libnet_name2addr4(l, argv[0], LIBNET_RESOLVE)) == -1)
 		usage();
 	
@@ -192,6 +216,13 @@
 		errx(1, "couldn't arp for host %s",
 		     libnet_addr2name4(target_ip, LIBNET_DONT_RESOLVE));
 	
+	if (poison_reverse) {
+		if (!arp_find(spoof_ip, &spoof_mac)) {
+			errx(1, "couldn't arp for spoof host %s",
+			     libnet_addr2name4(spoof_ip, LIBNET_DONT_RESOLVE));
+		}
+	}
+	
 	signal(SIGHUP, cleanup);
 	signal(SIGINT, cleanup);
 	signal(SIGTERM, cleanup);
@@ -200,6 +231,9 @@
 		arp_send(l, ARPOP_REPLY, NULL, spoof_ip,
 			 (target_ip ? (u_int8_t *)&target_mac : NULL),
 			 target_ip);
+		if (poison_reverse) {
+			arp_send(l, ARPOP_REPLY, NULL, target_ip, (uint8_t *)&spoof_mac, spoof_ip);
+		}
 		sleep(2);
 	}
 	/* NOTREACHED */