diff -urN strongswan-4.2.13/src/pluto/ipsec_doi.c strongswan-4.2.13-patched/src/pluto/ipsec_doi.c
--- strongswan-4.2.13/src/pluto/ipsec_doi.c	2009-03-21 09:41:49.000000000 +0100
+++ strongswan-4.2.13-patched/src/pluto/ipsec_doi.c	2009-03-21 09:50:06.000000000 +0100
@@ -5446,9 +5446,9 @@
    time_t tm = now();
     u_int32_t seqno;
 
-    if (!IS_ISAKMP_SA_ESTABLISHED(st->st_state))
+    if (!st || !IS_ISAKMP_SA_ESTABLISHED(st->st_state))
     {
-        loglog(RC_LOG_SERIOUS, "DPD: Received R_U_THERE for unestablished ISKAMP SA");
+        loglog(RC_LOG_SERIOUS, "DPD: Received R_U_THERE for unestablished ISAKMP SA");
         return STF_IGNORE;
     }
     if (n->isan_spisize != COOKIE_SIZE * 2 || pbs_left(pbs) < COOKIE_SIZE * 2)
@@ -5516,10 +5516,10 @@
 {
     u_int32_t seqno;
 
-    if (!IS_ISAKMP_SA_ESTABLISHED(st->st_state))
+    if (!st || !IS_ISAKMP_SA_ESTABLISHED(st->st_state))
     {
         loglog(RC_LOG_SERIOUS
-	    , "DPD: Received R_U_THERE_ACK for unestablished ISKAMP SA");
+	    , "DPD: Received R_U_THERE_ACK for unestablished ISAKMP SA");
         return STF_FAIL;
     }