Noté que todos los tutoriales que encontré para el acceso de Discourse a S3 concedían al usuario autoridad absoluta sobre el bucket: permiten la autoridad ‘s3:*’.
Esta es una política extremadamente imprudente, ya que otorga un control significativamente mayor sobre el bucket del que es razonable. Si estás utilizando S3 para el almacenamiento de copias de seguridad de Discourse, un atacante descontrolado podría eliminar tu bucket y tus copias de seguridad en su salida.
Hay dos formas de combatir esto: primero, una política más estricta…
… y segundo, aplicar algunas precauciones sensatas a la política del bucket. (Esto en realidad va más allá de lo que sería el mínimo necesario, pero estaba apurado y no tuve tiempo de experimentar, y es mejor que lo que encontré). Recomiendo activar el versionado y luego establecer una regla de ciclo de vida para las “versiones anteriores” que las elimine después de un tiempo razonable, como 21 días. La política dada permitiría la rotación de registros y la eliminación de archivos, pero no permitiría que el usuario con credenciales de S3 acceda para restaurar o eliminar versiones anteriores. Esto significa que, aunque podrían eliminar una copia de seguridad, un atacante descontrolado no podría borrarla del historial de versiones antes de que un administrador con credenciales root pueda recuperarla.
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.