From 8a8839e48efc5d3c7b2f6d40640b98766d63e724 Mon Sep 17 00:00:00 2001
From: Khashayar Fereidani <info@fereidani.com>
Date: Wed, 24 Jun 2026 09:14:20 +0000
Subject: [PATCH 1/2] Guard nil payload in decoded session messages on the
 client.

---
 client.go | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/client.go b/client.go
index 0404ca3..ed78dce 100644
--- a/client.go
+++ b/client.go
@@ -123,6 +123,13 @@ func handshakeWithServerSync(test *ethrTest, conn net.Conn) (startTime time.Time
 		err = os.ErrInvalid
 		return
 	}
+	// A SyncReady whose payload was omitted decodes with a nil SyncReady
+	// pointer; the Type check above does not prove otherwise.
+	if ethrMsg.SyncReady == nil {
+		ui.printDbg("Received SyncReady message with nil payload from Ethr server.")
+		err = os.ErrInvalid
+		return
+	}
 	delayNs := ethrMsg.SyncReady.DelayNs
 
 	if delayNs == 0 {
@@ -335,6 +342,14 @@ func tcpRunBandwidthTestSync(test *ethrTest, toStop chan int, duration time.Dura
 		toStop <- disconnect
 		return
 	}
+	// A SyncReady whose payload was omitted decodes with a nil SyncReady
+	// pointer; the Type check above does not prove otherwise.
+	if ethrMsg.SyncReady == nil {
+		ui.printErr("Received SyncReady message with nil payload from server.")
+		controlConn.Close()
+		toStop <- disconnect
+		return
+	}
 	delayNs := ethrMsg.SyncReady.DelayNs
 	rtt := recvTime.Sub(sendTime)
 	rttNs := rtt.Nanoseconds()

From b8b619a4976246be098b5b3fe8bdb9fe7e86b477 Mon Sep 17 00:00:00 2001
From: Khashayar Fereidani <info@fereidani.com>
Date: Wed, 24 Jun 2026 09:15:10 +0000
Subject: [PATCH 2/2] Use checked type assertions when parsing ICMP messages.

---
 client.go | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/client.go b/client.go
index ed78dce..fd9d60a 100644
--- a/client.go
+++ b/client.go
@@ -1130,7 +1130,12 @@ func icmpRecvMsg(c net.PacketConn, proto EthrProtocol, timeout time.Duration, ne
 			continue
 		}
 		if icmpMsg.Type == ipv4.ICMPTypeTimeExceeded || icmpMsg.Type == ipv6.ICMPTypeTimeExceeded {
-			body := icmpMsg.Body.(*icmp.TimeExceeded).Data
+			te, ok := icmpMsg.Body.(*icmp.TimeExceeded)
+			if !ok {
+				ui.printDbg("Received TimeExceeded ICMP message with unexpected body type.")
+				continue
+			}
+			body := te.Data
 			index := bytes.Index(body, neededSig[:4])
 			if index > 0 {
 				if proto == TCP {
@@ -1159,7 +1164,11 @@ func icmpRecvMsg(c net.PacketConn, proto EthrProtocol, timeout time.Duration, ne
 		}
 
 		if proto == ICMP && (icmpMsg.Type == ipv4.ICMPTypeEchoReply || icmpMsg.Type == ipv6.ICMPTypeEchoReply) {
-			echo := icmpMsg.Body.(*icmp.Echo)
+			echo, ok := icmpMsg.Body.(*icmp.Echo)
+			if !ok {
+				ui.printDbg("Received EchoReply ICMP message with unexpected body type.")
+				continue
+			}
 			ethrUnused(echo)
 			b, _ := icmpMsg.Body.Marshal(1)
 			if string(b[4:]) != string(neededIcmpBody) {