Agents can list tickets without permission
Agents can list tickets assigned to other agents in queues for which they don't have permissions.
Upgrade to the latest available OTRS patch level (https://ftp.otrs.org/pub/otrs/).
As a workaround, you can replace the affected files (see below for download).
ATTENTION: Please check if any of these files have been changed in your OTRS installation by additional add-ons. In that case you MUST NOT simply overwrite the files with the ones provided below. Please contact us instead.