diff --git a/.github/workflows/mirror.yml b/.github/workflows/mirror.yml
index 433624a31..6a5f396bd 100644
--- a/.github/workflows/mirror.yml
+++ b/.github/workflows/mirror.yml
@@ -8,6 +8,9 @@ on:
     branches:
       - 'main'
 
+# Declare default permissions as read only.
+permissions: read-all
+
 jobs:
   mirror_job:
     permissions: