diff --git a/examples/platforms/posix/flash.c b/examples/platforms/posix/flash.c
index 0650289fa..eb6ac91e8 100644
--- a/examples/platforms/posix/flash.c
+++ b/examples/platforms/posix/flash.c
@@ -78,7 +78,7 @@ otError utilsFlashInit(void)
         create = true;
     }
 
-    sFlashFd = open(fileName, O_RDWR | O_CREAT, 0666);
+    sFlashFd = open(fileName, O_RDWR | O_CREAT, 0600);
     lseek(sFlashFd, 0, SEEK_SET);
 
     otEXPECT_ACTION(sFlashFd >= 0, error = OT_ERROR_FAILED);
diff --git a/src/posix/platform/flash.c b/src/posix/platform/flash.c
index 999f396e0..3f415d203 100644
--- a/src/posix/platform/flash.c
+++ b/src/posix/platform/flash.c
@@ -80,7 +80,7 @@ otError utilsFlashInit(void)
         create = true;
     }
 
-    sFlashFd = open(fileName, O_RDWR | O_CREAT, 0666);
+    sFlashFd = open(fileName, O_RDWR | O_CREAT, 0600);
     lseek(sFlashFd, 0, SEEK_SET);
 
     otEXPECT_ACTION(sFlashFd >= 0, error = OT_ERROR_FAILED);