diff -uNr dhcp-3.1.2.ORIG/client/dhclient.c dhcp-3.1.2/client/dhclient.c
--- dhcp-3.1.2.ORIG/client/dhclient.c	2009-07-13 13:14:40.000000000 +0100
+++ dhcp-3.1.2/client/dhclient.c	2009-07-13 13:16:00.000000000 +0100
@@ -2550,8 +2550,9 @@
 					 (struct option_state *)0,
 					 lease -> options,
 					 &global_scope, oc, MDL)) {
-		if (data.len > 3) {
-			struct iaddr netmask, subnet, broadcast;
+		struct iaddr netmask;
+		if (data.len > 3 && data.len <= sizeof(netmask.iabuf)) {
+			struct iaddr subnet, broadcast;
 
 			memcpy (netmask.iabuf, data.data, data.len);
 			netmask.len = data.len;