Update CHANGELOG.md for 12.6.4

[ci skip]

CHANGELOG.md

@@ -2,6 +2,13 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
+## 12.6.4
+
+### Security (1 change)
+
+- Fix private objects exposure when using Project Import functionality.
+
+
 ## 12.6.2
 ### Security (6 changes)