Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 318867)
+++ channels/chan_sip.c	(working copy)
@@ -8417,8 +8417,8 @@
 		nextm = get_sdp_iterate(&next, req, "m");
 
 		/* Search for audio media definition */
-		if ((sscanf(m, "audio %30u/%30u RTP/%4s %n", &x, &numberofports, protocol, &len) == 3 && len > 0) ||
-		    (sscanf(m, "audio %30u RTP/%4s %n", &x, protocol, &len) == 2 && len > 0)) {
+		if ((sscanf(m, "audio %30u/%30u RTP/%4s %n", &x, &numberofports, protocol, &len) == 3 && len > 0 && x) ||
+		    (sscanf(m, "audio %30u RTP/%4s %n", &x, protocol, &len) == 2 && len > 0 && x)) {
 			if (!strcmp(protocol, "SAVP")) {
 				secure_audio = 1;
 			} else if (strcmp(protocol, "AVP")) {
@@ -8444,8 +8444,8 @@
 				ast_rtp_codecs_payloads_set_m_type(&newaudiortp, NULL, codec);
 			}
 		/* Search for video media definition */
-		} else if ((sscanf(m, "video %30u/%30u RTP/%4s %n", &x, &numberofports, protocol, &len) == 3 && len > 0) ||
-			   (sscanf(m, "video %30u RTP/%4s %n", &x, protocol, &len) == 2 && len >= 0)) {
+		} else if ((sscanf(m, "video %30u/%30u RTP/%4s %n", &x, &numberofports, protocol, &len) == 3 && len > 0 && x) ||
+			   (sscanf(m, "video %30u RTP/%4s %n", &x, protocol, &len) == 2 && len >= 0 && x)) {
 			if (!strcmp(protocol, "SAVP")) {
 				secure_video = 1;
 			} else if (strcmp(protocol, "AVP")) {
@@ -8471,8 +8471,8 @@
 				ast_rtp_codecs_payloads_set_m_type(&newvideortp, NULL, codec);
 			}
 		/* Search for text media definition */
-		} else if ((sscanf(m, "text %30u/%30u RTP/AVP %n", &x, &numberofports, &len) == 2 && len > 0) ||
-			   (sscanf(m, "text %30u RTP/AVP %n", &x, &len) == 1 && len > 0)) {
+		} else if ((sscanf(m, "text %30u/%30u RTP/AVP %n", &x, &numberofports, &len) == 2 && len > 0 && x) ||
+			   (sscanf(m, "text %30u RTP/AVP %n", &x, &len) == 1 && len > 0 && x)) {
 			text = TRUE;
 			p->notext = FALSE;
 			p->offered_media[SDP_TEXT].offered = TRUE;
@@ -8492,8 +8492,8 @@
 				ast_rtp_codecs_payloads_set_m_type(&newtextrtp, NULL, codec);
 			}
 		/* Search for image media definition */
-		} else if (p->udptl && ((sscanf(m, "image %30u udptl t38%n", &x, &len) == 1 && len > 0) ||
-					(sscanf(m, "image %30u UDPTL t38%n", &x, &len) == 1 && len > 0) )) {
+		} else if (p->udptl && ((sscanf(m, "image %30u udptl t38%n", &x, &len) == 1 && len > 0 && x) ||
+					(sscanf(m, "image %30u UDPTL t38%n", &x, &len) == 1 && len > 0 && x) )) {
 			image = TRUE;
 			if (debug)
 				ast_verbose("Got T.38 offer in SDP in dialog %s\n", p->callid);