The proper fix/workaround is to store objects with GUID keys in S3 only (actual file name stored in database) and then use content-disposition to emit correct file names later.

As @LostKobrakai discussed, you can consider sanitising/encoding the characters or changing them to hex representation, however there is no standardised way to pass string literal within JSON & there may be significant work required to handle these files.

I think only place in ex_aws to change would be to do this encoding/decoding transparently (as breaking change) in ExAws.Operation.S3.add_bucket_to_path/2 or maybe ratchet up a step and use XML for outgoing requests (so you get proper string literals that can represent the object names you need), however as it would create such huge support burden for the maintainers + is already discouraged by AWS + would encourage further bad application design, I don’t think it will be considered AT ALL

So my best suggestion is to change design as previously mentioned to obviate the need of this rigmarole. It is also the right thing to do, if you could sanitise the names with some kind of URI encoded string and avoid a whole class of security bugs… such as user putting a file name that effectively results in a path traversal exploit. The bigger the attack surface the more bigger your risk.