Atlassian has published the following security statement for providing cloud services that you can find at the following link: https://www.atlassian.com/trust/policies/cloud-security
External Share for Jira app STORES ONLY DATA provided by an Atlassian instance when installing the add-on. This data contains basic information for validating and enabling communication with a particular Atlassian instance.
Neither employees of Old Street Solutions Ltd. nor any other party is able to access the content of your Jira instance or any other your information except the information provided by the Atlassian Marketplace.
Effective as of 16th June 2019.