Manual:$wgDirectoryMode

Files and file uploads: $wgDirectoryMode
Default chmod permission value for newly created directories.
Introduced in version:1.13.0
Removed in version:Still in use
Allowed values:(integer between 0 and 0777 (octal))
Default value:511 (1.39+)
0777 (1.13-1.38)

Details

Default chmod permission value for newly created directories. Without quoting.

Don't forget to specify the leading 0, since this is an octal value.

On Windows, this value is ignored.

This is used by wfMkdirParents() to create image directories, among other things.