Affected: Octopus Deploy Octopus Server

In affected versions of Octopus Server it was possible for a user with sufficient access to set custom headers in all server responses. By submitting a specifically crafted referrer header the user could ensure that all subsequent server responses would return 500 errors rendering the site mostly unusable. The user would be able to subsequently set and unset the referrer header to control the denial of service state with a valid CSRF token whilst new CSRF tokens could not be generated.