diff --git a/core.lib b/core.lib
index 3787e138c6..1029889dc0 100644
--- a/core.lib
+++ b/core.lib
@@ -1 +1 @@
-https://github.com/mbedmicro/mbed/#bd2159db26273244d0e96714877174a32268060b
+https://github.com/mbedmicro/mbed/#d0db5c94e5ce899412280d8c71d65850e0c8b30b
diff --git a/drivers/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedPrint.c b/drivers/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedPrint.c
index 8542c211a5..cc760c5cfd 100644
--- a/drivers/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedPrint.c
+++ b/drivers/ESP8266Interface/ESP8266/ATParser/BufferedSerial/BufferedPrint.c
@@ -26,7 +26,10 @@ size_t BufferedSerialThunk(void *buf_serial, const void *s, size_t length);
 int BufferedPrintfC(void *stream, int size, const char* format, va_list arg)
 {
     int r;
-    char buffer[size];
+    char buffer[512];
+    if (size >= 512) {
+        return -1;
+    }
     memset(buffer, 0, size);
     r = vsprintf(buffer, format, arg);
     // this may not hit the heap but should alert the user anyways
diff --git a/features/storage/cfstore/source/cfstore_test.c b/features/storage/cfstore/source/cfstore_test.c
index 1e0929dde4..fbd907d6f1 100644
--- a/features/storage/cfstore/source/cfstore_test.c
+++ b/features/storage/cfstore/source/cfstore_test.c
@@ -346,7 +346,7 @@ int32_t cfstore_test_init_1(void)
     char* read_buf = NULL;
     const uint8_t key_name_max_len = CFSTORE_KEY_NAME_MAX_LENGTH+1;
     uint8_t key_name_len = 0;
-    char key_name_buf[key_name_max_len];
+    char key_name_buf[CFSTORE_KEY_NAME_MAX_LENGTH+1];
     int32_t ret = ARM_DRIVER_ERROR;
     ARM_CFSTORE_SIZE len = 0;
     ARM_CFSTORE_SIZE max_len = 0;