The Logs plugin before 3.0.4 for Craft CMS allows remote attackers to read arbitrary files via input to actionStream in Controller.php.

Files or Directories Accessible to External Parties in ether/logs

Ether Logs is a package that allows one to check one's logs in the Craft 3 utilities section. A vulnerability was found in versions prior to 3.0.4 that allowed authenticated admin users to access any file on the server. The vulnerability has been fixed in version 3.0.4. As a workaround, one may disable the plugin if untrustworthy sources have admin access.