If someone would generate a SHA1 CSR and submit it to an CA to receive a SHA2 certificate, would the process as a whole be at risk because the CSR could be malicious?
In this case, the “data” (as used in Q2) is the public key of the end user certificate. In practice the CA could still generate a SHA2 certificate, even when a SHA1 CSR is being submitted. However, the CSR itself would be vulnerable in theory. So if an attacker would get in between he could put another name on the certificate. However, a proper RA would validate the CN and discover the forgery.
So basically a collision at the CSR would be possible but the validation process around it would keep it safe. However, submitting a SHA-2 CSR would be safer.
Would this even be a real life attack scenario?