Since the vulnerability is exploited by a crafted binary file, I think that isn't something that CF's managed ruleset is able to protect against. They have the ability to scan incoming files with antivirus, but if the exploit is small and simple and can be mutated per request, I think it's unlikely any AV would pick it up.
I agree. And unstated in this write up is the direct upload route. Even if your Cloudflare was perfect, once the attacker got the preflight they send the binary file up to S3 directly and then hit the variant route directly. The first code to “validate” the upload was the exploitable libvips code.
Cloudflare or a WAF may or may not help. These can often catch and block specific bot traffic, but not every attack payload is delivered naively. It would be part of a defense in depth. Having the underlying vulnerability fixed is critically important. For those on AWS, WAF & Shield is also very useful but at the end of the day these let legitimate traffic through, such as legitimately uploading a file that only in its contents is malformed.