diff --git a/CHANGES b/CHANGES
index 1ea58e2f4f..f32714b60c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+4286.	[security]	render_ecs errors were mishandled when printing out
+			a OPT record resulting in a assertion failure.
+			(CVE-2015-8705) [RT #41397]
+
 4285.	[security]	Specific APL data could trigger a INSIST.
 			(CVE-2015-8704) [RT #41396]
 
diff --git a/doc/arm/notes.xml b/doc/arm/notes.xml
index 60108948b4..7c6afaf4f8 100644
--- a/doc/arm/notes.xml
+++ b/doc/arm/notes.xml
@@ -159,6 +159,14 @@
 	  by Brian Mitchell and is disclosed in CVE-2015-8704. [RT #41396]
 	</para>
       </listitem>
+      <listitem>
+	<para>
+	  render_ecs errors when printing out a OPT record were
+	  mishandled resulting in a assertion failure. This flaw
+	  was discovered by Brian Mitchell and is disclosed in
+	  CVE-2015-8705. [RT #41396]
+	</para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="relnotes_features"><info><title>New Features</title></info>
diff --git a/lib/dns/message.c b/lib/dns/message.c
index a30e5edf89..0fa0a0a4d8 100644
--- a/lib/dns/message.c
+++ b/lib/dns/message.c
@@ -3232,7 +3232,7 @@ dns_message_sectiontotext(dns_message_t *msg, dns_section_t section,
 }
 
 static isc_result_t
-render_ecs(isc_buffer_t *optbuf, isc_buffer_t *target) {
+render_ecs(isc_buffer_t *ecsbuf, isc_buffer_t *target) {
 	int i;
 	char addr[16], addr_text[64];
 	isc_uint16_t family;
@@ -3242,20 +3242,20 @@ render_ecs(isc_buffer_t *optbuf, isc_buffer_t *target) {
 	 * Note: This routine needs to handle malformed ECS options.
 	 */
 
-	if (isc_buffer_remaininglength(optbuf) < 4)
+	if (isc_buffer_remaininglength(ecsbuf) < 4)
 		return (DNS_R_OPTERR);
-	family = isc_buffer_getuint16(optbuf);
-	addrlen = isc_buffer_getuint8(optbuf);
-	scopelen = isc_buffer_getuint8(optbuf);
+	family = isc_buffer_getuint16(ecsbuf);
+	addrlen = isc_buffer_getuint8(ecsbuf);
+	scopelen = isc_buffer_getuint8(ecsbuf);
 
 	addrbytes = (addrlen + 7) / 8;
-	if (isc_buffer_remaininglength(optbuf) < addrbytes)
+	if (isc_buffer_remaininglength(ecsbuf) < addrbytes)
 		return (DNS_R_OPTERR);
 
 	ADD_STRING(target, ": ");
 	memset(addr, 0, sizeof(addr));
 	for (i = 0; i < addrbytes; i ++)
-		addr[i] = isc_buffer_getuint8(optbuf);
+		addr[i] = isc_buffer_getuint8(ecsbuf);
 
 	if (family == 1)
 		inet_ntop(AF_INET, addr, addr_text, sizeof(addr_text));
@@ -3358,9 +3358,18 @@ dns_message_pseudosectiontotext(dns_message_t *msg,
 			} else if (optcode == DNS_OPT_COOKIE) {
 				ADD_STRING(target, "; COOKIE");
 			} else if (optcode == DNS_OPT_CLIENT_SUBNET) {
+				isc_buffer_t ecsbuf;
+
 				ADD_STRING(target, "; CLIENT-SUBNET");
-				result = render_ecs(&optbuf, target);
+				isc_buffer_init(&ecsbuf,
+						isc_buffer_current(&optbuf),
+					        optlen);
+				isc_buffer_add(&ecsbuf, optlen);
+				result = render_ecs(&ecsbuf, target);
+				if (result == ISC_R_NOSPACE)
+					return (result);
 				if (result == ISC_R_SUCCESS) {
+					isc_buffer_forward(&optbuf, optlen);
 					ADD_STRING(target, "\n");
 					continue;
 				}