}
 		t.pendingPackets = t.pendingPackets[:0]
+		// Unblock writePacket if waiting for KEX.
+		t.writeCond.Broadcast()
 		t.mu.Unlock()
 	}
 
@@ -577,11 +594,20 @@ func (t *handshakeTransport) writePacket(p []byte) error {
 	}
 
 	if t.sentInitMsg != nil {
-		// Copy the packet so the writer can reuse the buffer.
-		cp := make([]byte, len(p))
-		copy(cp, p)
-		t.pendingPackets = append(t.pendingPackets, cp)
-		return nil
+		if len(t.pendingPackets) < maxPendingPackets {
+			// Copy the packet so the writer can reuse the buffer.
+			cp := make([]byte, len(p))
+			copy(cp, p)
+			t.pendingPackets = append(t.pendingPackets, cp)
+			return nil
+		}
+		for t.sentInitMsg != nil {
+			// Block and wait for KEX to complete or an error.
+			t.writeCond.Wait()
+			if t.writeError != nil {
+				return t.writeError
+			}
+		}
 	}
 
 	if t.writeBytesLeft > 0 {
@@ -598,6 +624,7 @@ func (t *handshakeTransport) writePacket(p []byte) error {
 
 	if err := t.pushPacket(p); err != nil {
 		t.writeError = err
+		t.writeCond.Broadcast()
 	}
 
 	return nil
diff --git a/vendor/modules.txt b/vendor/modules.txt
index 3479ba90..79a43779 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -688,8 +688,8 @@ go.opentelemetry.io/otel/metric/noop
 ## explicit; go 1.22
 go.opentelemetry.io/otel/trace
 go.opentelemetry.io/otel/trace/embedded
-# golang.org/x/crypto v0.33.0
-## explicit; go 1.20
+# golang.org/x/crypto v0.35.0
+## explicit; go 1.23.0
 golang.org/x/crypto/blowfish
 golang.org/x/crypto/cast5
 golang.org/x/crypto/chacha20