TLS 1.2 with CloudFront default domain - amazon-s3

Question

I have created a CloudFront distribution to front some publicly accessible content from an S3 origin. This is all fine, but I need to set the minimum supported TLS version to 1.2.
It seems that the only way to do this is to import a custom SSL certificate and set the ViewerCertificate properties, specifically the MinimumProtocolVersion. I can have Certificate Manager issue a public cert but I don't want to have to register a domain. For the purpose of this content, I'm happy with the default cloudfront.net domain.
It seems like specifying the minimum TLS version should be supported by default. Am I missing something here?
Thanks,
John

Answer 1

This might not be supported forever, but it turns out you can import a bogus, self-signed certificate for the default domain. CloudFront will ignore it, but will enforce your TLS policy.
For example, I'm currently testing this on d2uwa7ugi8xf89.cloudfront.net -- configured with security policy TLSv1.2_2019. openssl s_client will show that it's vending the default certificate:
% openssl s_client -servername d2uwa7ugi8xf89.cloudfront.net -tls1_2 -connect d2uwa7ugi8xf89.cloudfront.net:443
CONNECTED(00000003)
depth=3 C = US, O = "VeriSign, Inc.", OU = VeriSign Trust Network, OU = "(c) 2006 VeriSign, Inc. - For authorized use only", CN = VeriSign Class 3 Public Primary Certification Authority - G5
depth=2 C = US, O = DigiCert Inc, OU = www.digicert.com, CN = DigiCert Global Root G2
depth=1 C = US, O = DigiCert Inc, CN = DigiCert Global CA G2
depth=0 C = US, ST = Washington, L = Seattle, O = "Amazon.com, Inc.", CN = *.cloudfront.net
---
Certificate chain
0 s:/C=US/ST=Washington/L=Seattle/O=Amazon.com, Inc./CN=*.cloudfront.net
i:/C=US/O=DigiCert Inc/CN=DigiCert Global CA G2
1 s:/C=US/O=DigiCert Inc/CN=DigiCert Global CA G2
i:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert Global Root G2
2 s:/C=US/O=DigiCert Inc/OU=www.digicert.com/CN=DigiCert Global Root G2
i:/C=US/O=VeriSign, Inc./OU=VeriSign Trust Network/OU=(c) 2006 VeriSign, Inc. - For authorized use only/CN=VeriSign Class 3 Public Primary Certification Authority - G5
---
...
Attempt to connect with TLS 1.0 or TLS 1.1? No go:
% openssl s_client -servername d2uwa7ugi8xf89.cloudfront.net -tls1_1 -connect d2uwa7ugi8xf89.cloudfront.net:443
CONNECTED(00000003)
139725480863648:error:1409442E:SSL routines:ssl3_read_bytes:tlsv1 alert protocol version:s3_pkt.c:1493:SSL alert number 70
139725480863648:error:1409E0E5:SSL routines:ssl3_write_bytes:ssl handshake failure:s3_pkt.c:659:
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 7 bytes and written 0 bytes
---
New, (NONE), Cipher is (NONE)
...
This certificate was generated in the usual bogus self-signed certificate way:
openssl genrsa 2048 > cf.privkey
openssl req -new -subj /CN=d2uwa7ugi8xf89.cloudfront.net -key cf.privkey -out cf.csr
openssl x509 -in cf.csr -req -signkey cf.privkey -out cf.pem -days 99999