Ho notato che tutti i tutorial che ho trovato per l’accesso S3 di Discourse concedono all’utente un’autorità assoluta sul bucket: permettono l’autorità ‘s3:*’.
Questa è una politica estremamente sconsigliata, poiché concede un controllo sul bucket significativamente maggiore di quanto sia ragionevole. Se si utilizza S3 per l’archiviazione dei backup di Discourse, un attaccante impazzito potrebbe eliminare il bucket e i backup mentre se ne va.
Ci sono due modi per contrastare questo problema: uno, una policy più rigorosa…
… e due, applicare alcune precauzioni sensate alla policy del bucket. (Questa è in realtà ben oltre il minimo assoluto necessario, ma ero di fretta e non ho avuto tempo di sperimentare, ed è comunque meglio di quello che ho trovato). Consiglierei di attivare il versioning e quindi impostare una regola di ciclo di vita per le “versioni precedenti” che le elimini dopo un periodo ragionevole, come 21 giorni. La policy indicata consentirebbe la rotazione dei log e l’eliminazione dei file, ma non permetterebbe all’utente con credenziali S3 di ripristinare o eliminare definitivamente le versioni precedenti; ciò significa che, sebbene potrebbero eliminare un backup, un attaccante impazzito non potrebbe cancellarlo dalla cronologia delle versioni prima che un amministratore con credenziali root possa recuperarlo.
Oh, I’m sorry – I wasn’t trying to suggest you /should/ be; certainly I don’t know where you’d put it. I just found that when I Googled “Discourse S3 IAM” all of the example policies were the same awful wide-open one, so I’m reporting what I did instead of that.
(That’s why I seperated this thread from the other.)
Were those examples here on meta.discourse.org? If they’re in a howto you might be able to edit them, or you could draft your own and get it moved into #howto:sysadmin.
My take on this is that our responsibility for S3 advice is about the same as our advice on things like TLS configs (which we do update on occasion). We should try to stay “safe by default”, because we know that just about everyone’s going to blindly use whatever we suggest, because very few people know what any of this magic actually does. Our as-close-to-official-as-we-get guide on setting up S3 does suggest using the wide-open policy, so I’ll fix that up to be more sensible.
@Asher_Densmore-Lynn: if you find any other examples of problematic IAM policies floating around anywhere we can control (here on meta, git repos under the discourse GitHub user, that sort of thing), feel free to let us (me) know (with a specific reference to what’s problematic; everyone’s Google search results are different), and I’ll get it fixed.
Sure, and thanks! I hope you add the part about the bucket versioning – keeping your backups safe from catastrophe is hard to do when you have to allow rotation and deletion. If you need me to go into more detail or explain it better I’ll be happy to oblige.
One thing to bear in mind is that the howto I linked above is about asset upload, not backups. The policy required for that is likely to be somewhat different to one required for backups. Also, that howto assumes that Discourse will be creating the bucket, and adding instructions on manually adding versioning and rotation would significantly complicate what is already a bit of a bear of a process. If the versioning/rotation settings can be set at creation time (without opening up the IAM policy to allow an attacker to remove those attributes later), then a PR to Discourse to add that ability (even by default) wouldn’t be a bad idea. Otherwise, I think it’s best if you write a separate “Discourse S3 201: Securitay!” topic, that can be linked from the main howto.
I looked at that setup guide – be aware that that bucket creation will fail with those permissions. You’ll want to add s3:CreateBucket if that’s something you want to keep.