A little backstory
A few weeks ago, I decided to build a little tool for my Synology Download Station, since I was not quite satisfied with the features DS Download offered me for simple monitoring. However, while testing out the API as it was documented in official API docs, I stumbled upon some rather unusual behaviour, that allows you to access details of any download task, even if it does not belong to the user you're authenticated as.
While this actually is a security issue, as Synology confirmed upon my report, I do not think that users would rate their download tasks crucial information. And those who do might not even share their Download Station access with other users to begin with. So while this is obviously a bug that needs to - and according to their response will be - fixed, it is not a terrible leak but more of a reminder of an age old discussion.
The tale of incremental ID's
There have been numerous discussion about this topic in the past, and I think this little bug is a good reminder of why you should not use incremental ID's. If we break our System down to the very basic, whatever it may be, as soon as it involves access control, there are two main factors that decide whether or not a user can access a certain resource: