diff --git a/src/amf/ngap-path.c b/src/amf/ngap-path.c
index b7094a053..0c3488d24 100644
--- a/src/amf/ngap-path.c
+++ b/src/amf/ngap-path.c
@@ -200,6 +200,7 @@ int ngap_send_to_nas(ran_ue_t *ran_ue,
     default:
         ogs_error("Not implemented(security header type:0x%x)",
                 sh->security_header_type);
+        ran_ue_remove(ran_ue);
         return OGS_ERROR;
     }
 
@@ -207,12 +208,39 @@ int ngap_send_to_nas(ran_ue_t *ran_ue,
         if (nas_5gs_security_decode(ran_ue->amf_ue,
                 security_header_type, nasbuf) != OGS_OK) {
             ogs_error("nas_eps_security_decode failed()");
+            ran_ue_remove(ran_ue);
             return OGS_ERROR;
         }
     }
 
     h = (ogs_nas_5gmm_header_t *)nasbuf->data;
     ogs_assert(h);
+    if (procedureCode == NGAP_ProcedureCode_id_InitialUEMessage) {
+        if (h->extended_protocol_discriminator !=
+                OGS_NAS_EXTENDED_PROTOCOL_DISCRIMINATOR_5GMM) {
+
+            ogs_error("Invalid extended_protocol_discriminator [%d]",
+                    h->extended_protocol_discriminator);
+
+            ogs_pkbuf_free(nasbuf);
+            ran_ue_remove(ran_ue);
+
+            return OGS_ERROR;
+        }
+
+        if (h->message_type != OGS_NAS_5GS_REGISTRATION_REQUEST &&
+            h->message_type != OGS_NAS_5GS_SERVICE_REQUEST &&
+            h->message_type != OGS_NAS_5GS_DEREGISTRATION_REQUEST_FROM_UE) {
+
+            ogs_error("Invalid 5GMM message type [%d]", h->message_type);
+
+            ogs_pkbuf_free(nasbuf);
+            ran_ue_remove(ran_ue);
+
+            return OGS_ERROR;
+        }
+    }
+
     if (h->extended_protocol_discriminator ==
             OGS_NAS_EXTENDED_PROTOCOL_DISCRIMINATOR_5GMM) {
         e = amf_event_new(AMF_EVENT_5GMM_MESSAGE);
@@ -247,7 +275,10 @@ int ngap_send_to_nas(ran_ue_t *ran_ue,
     } else {
         ogs_error("Unknown NAS Protocol discriminator 0x%02x",
                   h->extended_protocol_discriminator);
+
         ogs_pkbuf_free(nasbuf);
+        ran_ue_remove(ran_ue);
+
         return OGS_ERROR;
     }
 }
diff --git a/src/mme/s1ap-handler.c b/src/mme/s1ap-handler.c
index 8f2147563..dff401ded 100644
--- a/src/mme/s1ap-handler.c
+++ b/src/mme/s1ap-handler.c
@@ -586,10 +586,8 @@ void s1ap_handle_initial_ue_message(mme_enb_t *enb, ogs_s1ap_message_t *message)
         enb_ue->enb_ue_s1ap_id, enb_ue->mme_ue_s1ap_id,
         enb_ue->saved.tai.tac, enb_ue->saved.e_cgi.cell_id);
 
-    r = s1ap_send_to_nas(enb_ue,
-            S1AP_ProcedureCode_id_initialUEMessage, NAS_PDU);
-    ogs_expect(r == OGS_OK);
-    ogs_assert(r != OGS_ERROR);
+    ogs_expect(OGS_OK == s1ap_send_to_nas(
+                enb_ue, S1AP_ProcedureCode_id_initialUEMessage, NAS_PDU));
 }
 
 void s1ap_handle_uplink_nas_transport(
@@ -777,10 +775,8 @@ void s1ap_handle_uplink_nas_transport(
         ogs_error("No UE Context in UplinkNASTransport");
     }
 
-    r = s1ap_send_to_nas(enb_ue,
-            S1AP_ProcedureCode_id_uplinkNASTransport, NAS_PDU);
-    ogs_expect(r == OGS_OK);
-    ogs_assert(r != OGS_ERROR);
+    ogs_expect(OGS_OK == s1ap_send_to_nas(
+                enb_ue, S1AP_ProcedureCode_id_uplinkNASTransport, NAS_PDU));
 }
 
 void s1ap_handle_ue_capability_info_indication(
diff --git a/src/mme/s1ap-path.c b/src/mme/s1ap-path.c
index 2123aad17..c47bb5e37 100644
--- a/src/mme/s1ap-path.c
+++ b/src/mme/s1ap-path.c
@@ -207,6 +207,7 @@ int s1ap_send_to_nas(enb_ue_t *enb_ue,
     default:
         ogs_error("Not implemented(security header type:0x%x)",
                 sh->security_header_type);
+        enb_ue_remove(enb_ue);
         return OGS_ERROR;
     }
 
@@ -214,12 +215,42 @@ int s1ap_send_to_nas(enb_ue_t *enb_ue,
         if (nas_eps_security_decode(enb_ue->mme_ue,
                 security_header_type, nasbuf) != OGS_OK) {
             ogs_error("nas_eps_security_decode failed()");
+            enb_ue_remove(enb_ue);
             return OGS_ERROR;
         }
     }
 
     h = (ogs_nas_emm_header_t *)nasbuf->data;
     ogs_assert(h);
+
+    if (procedureCode == S1AP_ProcedureCode_id_initialUEMessage) {
+        if (h->protocol_discriminator != OGS_NAS_PROTOCOL_DISCRIMINATOR_EMM) {
+
+            ogs_error("Invalid protocol_discriminator [%d]",
+                    h->protocol_discriminator);
+
+            ogs_pkbuf_free(nasbuf);
+            enb_ue_remove(enb_ue);
+
+            return OGS_ERROR;
+        }
+
+        if (h->security_header_type !=
+                OGS_NAS_SECURITY_HEADER_FOR_SERVICE_REQUEST_MESSAGE &&
+            h->message_type != OGS_NAS_EPS_ATTACH_REQUEST &&
+            h->message_type != OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST &&
+            h->message_type != OGS_NAS_EPS_EXTENDED_SERVICE_REQUEST &&
+            h->message_type != OGS_NAS_EPS_DETACH_REQUEST) {
+
+            ogs_error("Invalid EMM message type [%d]", h->message_type);
+
+            ogs_pkbuf_free(nasbuf);
+            enb_ue_remove(enb_ue);
+
+            return OGS_ERROR;
+        }
+    }
+
     if (h->protocol_discriminator == OGS_NAS_PROTOCOL_DISCRIMINATOR_EMM) {
         int rv;
         e = mme_event_new(MME_EVENT_EMM_MESSAGE);
@@ -255,7 +286,10 @@ int s1ap_send_to_nas(enb_ue_t *enb_ue,
     } else {
         ogs_error("Unknown/Unimplemented NAS Protocol discriminator 0x%02x",
                   h->protocol_discriminator);
+
         ogs_pkbuf_free(nasbuf);
+        enb_ue_remove(enb_ue);
+
         return OGS_ERROR;
     }
 }
diff --git a/tests/attach/issues-test.c b/tests/attach/issues-test.c
index b1fd2fd42..316737a17 100644
--- a/tests/attach/issues-test.c
+++ b/tests/attach/issues-test.c
@@ -1862,6 +1862,7 @@ static void issues_2287_v264_func(abts_case *tc, void *data)
     test_ue_remove_all();
 }
 
+#if 0 /* Deprecated to resolve issue #3131 */
 static void pull_3122_v270_func(abts_case *tc, void *data)
 {
     int rv;
@@ -1973,6 +1974,7 @@ static void pull_3122_v270_func(abts_case *tc, void *data)
 
     test_ue_remove(test_ue);
 }
+#endif
 
 abts_suite *test_issues(abts_suite *suite)
 {
@@ -1981,7 +1983,9 @@ abts_suite *test_issues(abts_suite *suite)
     abts_run_test(suite, issues_1431_func, NULL);
     abts_run_test(suite, issues_2287_v263_func, NULL);
     abts_run_test(suite, issues_2287_v264_func, NULL);
+#if 0 /* Deprecated to resolve issue #3131 */
     abts_run_test(suite, pull_3122_v270_func, NULL);
+#endif
 
     return suite;
 }
diff --git a/tests/registration/identity-test.c b/tests/registration/identity-test.c
index 17fd9ac53..e80bb5836 100644
--- a/tests/registration/identity-test.c
+++ b/tests/registration/identity-test.c
@@ -354,6 +354,7 @@ static void test1_func(abts_case *tc, void *data)
     test_ue_remove(test_ue);
 }
 
+#if 0 /* Deprecated to resolve issue #3131 */
 static void pull_3122_v270_func(abts_case *tc, void *data)
 {
     int rv;
@@ -469,13 +470,16 @@ static void pull_3122_v270_func(abts_case *tc, void *data)
     /* Clear Test UE Context */
     test_ue_remove(test_ue);
 }
+#endif
 
 abts_suite *test_identity(abts_suite *suite)
 {
     suite = ADD_SUITE(suite)
 
     abts_run_test(suite, test1_func, NULL);
+#if 0 /* Deprecated to resolve issue #3131 */
     abts_run_test(suite, pull_3122_v270_func, NULL);
+#endif
 
     return suite;
 }