The remote Bitbucket server is affected by an unauthorized access attack vector.
Versions of Bitbucket 4.x, prior to 4.12.0 contain a flaw that is due to the program failing to properly enforce access permission requirements for the Default Reviewer admin page. This may allow an authenticated remote attacker to gain unauthorized access to this page, where they may e.g. add or remove default reviewers.
Upgrade to Bitbucket version 4.12.0 or later.