diff --git a/package/rtl8821au/0003-Fix-using-sprintf-for-extending-string-which-causes-.patch b/package/rtl8821au/0003-Fix-using-sprintf-for-extending-string-which-causes-.patch
new file mode 100644
index 0000000000..6753eefdd9
--- /dev/null
+++ b/package/rtl8821au/0003-Fix-using-sprintf-for-extending-string-which-causes-.patch
@@ -0,0 +1,336 @@
+From cc3262a32ce326d89d597bb8557ce0da05240e98 Mon Sep 17 00:00:00 2001
+From: Coleman <omegacoleman@gmail.com>
+Date: Fri, 17 Jul 2020 08:53:00 +0800
+Subject: [PATCH 3/3] Fix using sprintf for extending string, which causes
+ undefined behavior. (#334)
+
+---
+ core/rtw_mp.c              |   2 +-
+ os_dep/linux/ioctl_linux.c | 108 ++++++++++++++++++-------------------
+ 2 files changed, 55 insertions(+), 55 deletions(-)
+
+diff --git a/core/rtw_mp.c b/core/rtw_mp.c
+index c2e400d..989bb3e 100644
+--- a/core/rtw_mp.c
++++ b/core/rtw_mp.c
+@@ -1871,7 +1871,7 @@ u32 mp_query_psd(PADAPTER pAdapter, u8 *data)
+ 		} else {
+ 			psd_data = rtw_GetPSDData(pAdapter, i);
+ 		}
+-		sprintf(data, "%s%x ", data, psd_data);
++		sprintf(data + strlen(data), "%x ", psd_data);
+ 		i++;
+ 	}
+ 
+diff --git a/os_dep/linux/ioctl_linux.c b/os_dep/linux/ioctl_linux.c
+index c74a153..9543fa3 100644
+--- a/os_dep/linux/ioctl_linux.c
++++ b/os_dep/linux/ioctl_linux.c
+@@ -9080,19 +9080,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i = 0; i < EFUSE_MAP_SIZE; i += 16) {
+ //			DBG_871X("0x%02x\t", i);
+-			sprintf(extra, "%s0x%02x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%02x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, PROMContent[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", PROMContent[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra, "%s\t", extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, PROMContent[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", PROMContent[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra,"%s\n",extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0], "realmap") == 0) {
+@@ -9107,19 +9107,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i = 0; i < EFUSE_MAP_SIZE; i += 16) {
+ //			DBG_871X("0x%02x\t", i);
+-			sprintf(extra, "%s0x%02x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%02x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra, "%s\t", extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra,"%s\n",extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0], "rmap") == 0) {
+@@ -9158,7 +9158,7 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		*extra = 0;
+ 		for (i=0; i<cnts; i++) {
+ //			DBG_871X("0x%02x ", data[i]);
+-			sprintf(extra, "%s0x%02X ", extra, data[i]);
++			sprintf(extra + strlen(extra), "0x%02X ", data[i]);
+ 		}
+ //		DBG_871X("}\n");
+ 	} else if (strcmp(tmp[0], "realraw") == 0) {
+@@ -9174,17 +9174,17 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n0x00\t");
+ 		for (i=0; i< mapLen; i++) {
+ 			//			DBG_871X("%02X", rawdata[i]);
+-			sprintf(extra, "%s%02X", extra, rawdata[i]);
++			sprintf(extra + strlen(extra), "%02X", rawdata[i]);
+ 			if ((i & 0xF) == 0xF) {
+ 				//				DBG_871X("\n");
+-				sprintf(extra, "%s\n", extra);
+-				sprintf(extra, "%s0x%02x\t", extra, i+1);
++				sprintf(extra + strlen(extra), "\n");
++				sprintf(extra + strlen(extra), "0x%02x\t", i+1);
+ 			} else if ((i & 0x7) == 0x7) {
+ 				//				DBG_871X("\t");
+-				sprintf(extra, "%s \t", extra);
++				sprintf(extra + strlen(extra), " \t");
+ 			} else {
+ 				//				DBG_871X(" ");
+-				sprintf(extra, "%s ", extra);
++				sprintf(extra + strlen(extra), " ");
+ 			}
+ 		}
+ 		//		DBG_871X("}\n");
+@@ -9269,10 +9269,10 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		*extra = 0;
+ 		for (i=0; i<cnts; i++) {
+ //			DBG_871X("%02X", data[i]);
+-			sprintf(extra, "%s%02X", extra, data[i]);
++			sprintf(extra + strlen(extra), "%02X", data[i]);
+ 			if (i != (cnts-1)) {
+ //				DBG_871X(":");
+-				sprintf(extra,"%s:",extra);
++				sprintf(extra + strlen(extra), ":");
+ 			}
+ 		}
+ //		DBG_871X("}\n");
+@@ -9330,10 +9330,10 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		*extra = 0;
+ 		for (i=0; i<cnts; i++) {
+ //			DBG_871X("0x%02x", data[i]);
+-			sprintf(extra, "%s0x%02X", extra, data[i]);
++			sprintf(extra + strlen(extra), "0x%02X", data[i]);
+ 			if (i != (cnts-1)) {
+ //				DBG_871X(",");
+-				sprintf(extra,"%s,",extra);
++				sprintf(extra + strlen(extra), ",");
+ 			}
+ 		}
+ //		DBG_871X("}\n");
+@@ -9355,19 +9355,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i=0; i<512; i+=16) { // set 512 because the iwpriv's extra size have limit 0x7FF
+ //			DBG_871X("0x%03x\t", i);
+-			sprintf(extra, "%s0x%03x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%03x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->BTEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra,"%s\t",extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->BTEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra, "%s\n", extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0],"btbmap") == 0) {
+@@ -9384,19 +9384,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i=512; i<1024 ; i+=16) {
+ //			DBG_871X("0x%03x\t", i);
+-			sprintf(extra, "%s0x%03x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%03x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->BTEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra,"%s\t",extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", data[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->BTEfuseInitMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->BTEfuseInitMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra, "%s\n", extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0],"btrmap") == 0) {
+@@ -9436,7 +9436,7 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ //		DBG_871X("%s: bt efuse data={", __FUNCTION__);
+ 		for (i=0; i<cnts; i++) {
+ //			DBG_871X("0x%02x ", data[i]);
+-			sprintf(extra, "%s 0x%02X ", extra, data[i]);
++			sprintf(extra + strlen(extra), " 0x%02X ", data[i]);
+ 		}
+ //		DBG_871X("}\n");
+ 		DBG_871X(FUNC_ADPT_FMT ": BT MAC=[%s]\n", FUNC_ADPT_ARG(padapter), extra);
+@@ -9445,19 +9445,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i=0; i<512; i+=16) {
+ //			DBG_871X("0x%03x\t", i);
+-			sprintf(extra, "%s0x%03x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%03x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra, "%s\t", extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra, "%s\n", extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0],"btbfake") == 0) {
+@@ -9465,19 +9465,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i=512; i<1024; i+=16) {
+ //			DBG_871X("0x%03x\t", i);
+-			sprintf(extra, "%s0x%03x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%03x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra, "%s\t", extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeBTEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra, "%s\n", extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 	} else if (strcmp(tmp[0],"wlrfkmap")== 0) {
+@@ -9485,19 +9485,19 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		sprintf(extra, "\n");
+ 		for (i=0; i<EFUSE_MAP_SIZE; i+=16) {
+ //			DBG_871X("\t0x%02x\t", i);
+-			sprintf(extra, "%s0x%02x\t", extra, i);
++			sprintf(extra + strlen(extra), "0x%02x\t", i);
+ 			for (j=0; j<8; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s%02X ", extra, pEfuseHal->fakeEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), "%02X ", pEfuseHal->fakeEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\t");
+-			sprintf(extra, "%s\t", extra);
++			sprintf(extra + strlen(extra), "\t");
+ 			for (; j<16; j++) {
+ //				DBG_871X("%02X ", pEfuseHal->fakeEfuseModifiedMap[i+j]);
+-				sprintf(extra, "%s %02X", extra, pEfuseHal->fakeEfuseModifiedMap[i+j]);
++				sprintf(extra + strlen(extra), " %02X", pEfuseHal->fakeEfuseModifiedMap[i+j]);
+ 			}
+ //			DBG_871X("\n");
+-			sprintf(extra, "%s\n", extra);
++			sprintf(extra + strlen(extra), "\n");
+ 		}
+ //		DBG_871X("\n");
+ 
+@@ -9523,7 +9523,7 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		*extra = 0;
+ 		for (i=0; i<cnts; i++) {
+ 			DBG_871X("wlrfkrmap = 0x%02x \n", pEfuseHal->fakeEfuseModifiedMap[addr+i]);
+-			sprintf(extra, "%s0x%02X ", extra, pEfuseHal->fakeEfuseModifiedMap[addr+i]);
++			sprintf(extra + strlen(extra), "0x%02X ", pEfuseHal->fakeEfuseModifiedMap[addr+i]);
+ 		}
+ 	} else if (strcmp(tmp[0],"btrfkrmap")== 0) {
+ 		if ((tmp[1]==NULL) || (tmp[2]==NULL)) {
+@@ -9547,7 +9547,7 @@ static int rtw_mp_efuse_get(struct net_device *dev,
+ 		*extra = 0;
+ 		for (i=0; i<cnts; i++) {
+ 			DBG_871X("wlrfkrmap = 0x%02x \n", pEfuseHal->fakeBTEfuseModifiedMap[addr+i]);
+-			sprintf(extra, "%s0x%02X ", extra, pEfuseHal->fakeBTEfuseModifiedMap[addr+i]);
++			sprintf(extra + strlen(extra), "0x%02X ", pEfuseHal->fakeBTEfuseModifiedMap[addr+i]);
+ 		}
+ 	} else {
+ 		sprintf(extra, "Command not found!");
+@@ -10409,7 +10409,7 @@ static int rtw_mp_read_reg(struct net_device *dev,
+ 			pnext++;
+ 			if ( *pnext != '\0' ) {
+ 				strtout = simple_strtoul (pnext , &ptmp, 16);
+-				sprintf( extra, "%s %d" ,extra ,strtout );
++				sprintf(extra + strlen(extra), " %d"  ,strtout );
+ 			} else {
+ 				break;
+ 			}
+@@ -10443,7 +10443,7 @@ static int rtw_mp_read_reg(struct net_device *dev,
+ 			pnext++;
+ 			if ( *pnext != '\0' ) {
+ 				strtout = simple_strtoul (pnext , &ptmp, 16);
+-				sprintf( extra, "%s %d" ,extra ,strtout );
++				sprintf(extra + strlen(extra), " %d"  ,strtout );
+ 			} else {
+ 				break;
+ 			}
+@@ -10566,7 +10566,7 @@ static int rtw_mp_read_rf(struct net_device *dev,
+ 		pnext++;
+ 		if ( *pnext != '\0' ) {
+ 			strtou = simple_strtoul (pnext , &ptmp, 16);
+-			sprintf( extra, "%s %d" ,extra ,strtou );
++			sprintf(extra + strlen(extra), " %d"  ,strtou );
+ 		} else {
+ 			break;
+ 		}
+@@ -12155,14 +12155,14 @@ todo:
+ 				goto exit;
+ 
+ #ifdef CONFIG_RTL8723A
+-			sprintf(extra, "%s %d ", extra, (pMptCtx->mptOutBuf[i]& 0x3f));
++			sprintf(extra + strlen(extra), " %d ", (pMptCtx->mptOutBuf[i]& 0x3f));
+ #else
+-			sprintf(extra, "%s %d ", extra, (pMptCtx->mptOutBuf[i]& 0x1f));
++			sprintf(extra + strlen(extra), " %d ", (pMptCtx->mptOutBuf[i]& 0x1f));
+ #endif
+ 		}
+ 	} else {
+ 		for (i=4; i<pMptCtx->mptOutLen; i++) {
+-			sprintf(extra, "%s 0x%x ", extra, pMptCtx->mptOutBuf[i]);
++			sprintf(extra + strlen(extra), " 0x%x ", pMptCtx->mptOutBuf[i]);
+ 		}
+ 	}
+ 
+-- 
+2.27.0
+
