diff --git a/src/Cedar/DDNS.h b/src/Cedar/DDNS.h
index 0775766f..c8fa0207 100644
--- a/src/Cedar/DDNS.h
+++ b/src/Cedar/DDNS.h
@@ -43,7 +43,7 @@
 #define	DDNS_URL2_V4_ALT	"http://get-my-ip.ddns.uxcom.jp/ddns/getmyip.ashx"
 #define	DDNS_URL2_V6_ALT	"http://get-my-ip-v6.ddns.uxcom.jp/ddns/getmyip.ashx"
 
-#define	DDNS_RPC_MAX_RECV_SIZE				DYN32(DDNS_RPC_MAX_RECV_SIZE, (128 * 1024 * 1024))
+#define	DDNS_RPC_MAX_RECV_SIZE				DYN32(DDNS_RPC_MAX_RECV_SIZE, (38 * 1024 * 1024))
 
 // Connection Timeout
 #define	DDNS_CONNECT_TIMEOUT		DYN32(DDNS_CONNECT_TIMEOUT, (15 * 1000))
diff --git a/src/Mayaqua/Memory.c b/src/Mayaqua/Memory.c
index 96ff994a..aa793d70 100644
--- a/src/Mayaqua/Memory.c
+++ b/src/Mayaqua/Memory.c
@@ -3114,6 +3114,10 @@ void AdjustBufSize(BUF *b, UINT new_size)
 
 	while (b->SizeReserved < new_size)
 	{
+		if (b->SizeReserved > 0x7FFFFFFF)
+		{
+			AbortExitEx("AdjustBufSize(): too large buffer size");
+		}
 		b->SizeReserved = b->SizeReserved * 2;
 	}
 	b->Buf = ReAlloc(b->Buf, b->SizeReserved);
diff --git a/src/Mayaqua/Network.c b/src/Mayaqua/Network.c
index 04aebdea..b170d130 100644
--- a/src/Mayaqua/Network.c
+++ b/src/Mayaqua/Network.c
@@ -1191,7 +1191,9 @@ void RUDPProcess_NatT_Recv(RUDP_STACK *r, UDPPACKET *udp)
 		bool is_ok = PackGetBool(p, "ok");
 		UINT64 tran_id = PackGetInt64(p, "tran_id");
 
-		ExtractAndApplyDynList(p);
+		// This ExtractAndApplyDynList() calling was removed because it is not actually used and could be abused by
+		// illegal UDP packets that spoof the source IP address. 2023-6-14 Daiyuu Nobori
+		// ExtractAndApplyDynList(p);
 
 		if (r->ServerMode)
 		{