> HIGH Severity. This includes issues that are of a lower risk than critical, perhaps due to affecting less common configurations, or which are less likely to be exploitable. These issues will be kept private and will trigger a new release of all supported versions. We will attempt to keep the time these issues are private to a minimum; our aim would be no longer than a month where this is something under our control

So something to make sure you update, but not a Heartbleed level concern