diff --git a/libraries/FS/src/vfs_api.cpp b/libraries/FS/src/vfs_api.cpp
index ab7dccb7599..e65a537c03d 100644
--- a/libraries/FS/src/vfs_api.cpp
+++ b/libraries/FS/src/vfs_api.cpp
@@ -36,7 +36,8 @@ FileImplPtr VFSImpl::open(const char* fpath, const char* mode, const bool create
         return FileImplPtr();
     }
 
-    sprintf(temp,"%s%s", _mountpoint, fpath);
+    strcpy(temp, _mountpoint);
+    strcat(temp, fpath);
 
     struct stat st;
     //file found
@@ -136,19 +137,25 @@ bool VFSImpl::rename(const char* pathFrom, const char* pathTo)
         log_e("%s does not exists", pathFrom);
         return false;
     }
-    char * temp1 = (char *)malloc(strlen(pathFrom)+strlen(_mountpoint)+1);
+    size_t mountpointLen = strlen(_mountpoint);
+    char * temp1 = (char *)malloc(strlen(pathFrom)+mountpointLen+1);
     if(!temp1) {
         log_e("malloc failed");
         return false;
     }
-    char * temp2 = (char *)malloc(strlen(pathTo)+strlen(_mountpoint)+1);
+    char * temp2 = (char *)malloc(strlen(pathTo)+mountpointLen+1);
     if(!temp2) {
         free(temp1);
         log_e("malloc failed");
         return false;
     }
-    sprintf(temp1,"%s%s", _mountpoint, pathFrom);
-    sprintf(temp2,"%s%s", _mountpoint, pathTo);
+
+    strcpy(temp1, _mountpoint);
+    strcat(temp1, pathFrom);
+
+    strcpy(temp2, _mountpoint);
+    strcat(temp2, pathTo);
+
     auto rc = ::rename(temp1, temp2);
     free(temp1);
     free(temp2);
@@ -182,7 +189,10 @@ bool VFSImpl::remove(const char* fpath)
         log_e("malloc failed");
         return false;
     }
-    sprintf(temp,"%s%s", _mountpoint, fpath);
+
+    strcpy(temp, _mountpoint);
+    strcat(temp, fpath);
+
     auto rc = unlink(temp);
     free(temp);
     return rc == 0;
@@ -211,7 +221,10 @@ bool VFSImpl::mkdir(const char *fpath)
         log_e("malloc failed");
         return false;
     }
-    sprintf(temp,"%s%s", _mountpoint, fpath);
+
+    strcpy(temp, _mountpoint);
+    strcat(temp, fpath);
+
     auto rc = ::mkdir(temp, ACCESSPERMS);
     free(temp);
     return rc == 0;
@@ -244,7 +257,10 @@ bool VFSImpl::rmdir(const char *fpath)
         log_e("malloc failed");
         return false;
     }
-    sprintf(temp,"%s%s", _mountpoint, fpath);
+
+    strcpy(temp, _mountpoint);
+    strcat(temp, fpath);
+
     auto rc = ::rmdir(temp);
     free(temp);
     return rc == 0;
@@ -265,7 +281,9 @@ VFSFileImpl::VFSFileImpl(VFSImpl* fs, const char* fpath, const char* mode)
     if(!temp) {
         return;
     }
-    sprintf(temp,"%s%s", _fs->_mountpoint, fpath);
+
+    strcpy(temp, _fs->_mountpoint);
+    strcat(temp, fpath);
 
     _path = strdup(fpath);
     if(!_path) {
@@ -362,7 +380,10 @@ void VFSFileImpl::_getStat() const
     if(!temp) {
         return;
     }
-    sprintf(temp,"%s%s", _fs->_mountpoint, _path);
+
+    strcpy(temp, _fs->_mountpoint);
+    strcat(temp, _path);
+
     if(!stat(temp, &_stat)) {
         _written = false;
     }
@@ -466,14 +487,27 @@ FileImplPtr VFSFileImpl::openNextFile(const char* mode)
     if(file->d_type != DT_REG && file->d_type != DT_DIR) {
         return openNextFile(mode);
     }
-    String fname = String(file->d_name);
-    String name = String(_path);
-    if(!fname.startsWith("/") && !name.endsWith("/")) {
-        name += "/";
+
+    size_t pathLen = strlen(_path);
+    size_t fileNameLen = strlen(file->d_name);
+    char * name = (char *)malloc(pathLen+fileNameLen+2);
+
+    if(name == NULL) {
+        return FileImplPtr();
     }
-    name += fname;
 
-    return std::make_shared<VFSFileImpl>(_fs, name.c_str(), mode);
+    strcpy(name, _path);
+
+    if ((file->d_name[0] != '/') && (_path[pathLen - 1] != '/'))
+    {
+        strcat(name, "/");
+    }
+
+    strcat(name, file->d_name);
+
+    FileImplPtr fileImplPtr = std::make_shared<VFSFileImpl>(_fs, name, mode);
+    free(name);
+    return fileImplPtr;
 }
 
 boolean VFSFileImpl::seekDir(long position){