Server 2022 TLS 1.3 makes A+ go to A rating

[Marcel-Balk]

Today we tested with Windows Server 2022 on a test enviroment and when TLS 1.3 is disabled ( TLS_AES_256_GCM_SHA384 / TLS_AES_256_GCM_SHA384 ) We are getting a status of A+ on the page https://shorturl.at/bevE9

When we enable TLS 1.3 the status is going to A what should not be happening.
Can this be fixed ?

[RobTho]

Hi
i guess it is caused by missing "Downgrade attack prevention"
If only TLS 1.2 enabled there is nothing to downgrade, so protection against this is don't care.
If TLS 1.3 and TLS 1.2 is enabled and no "Downgrade attack prevention" you will be set down to "A" only.
As far as i know MS do not support "Downgrade attack prevention" but maybe changed with 2022.

[Marcel-Balk]

But TLS 1.2 and TLS 1.3 are secure so why the A and not A+ ?

[Marcel-Balk]

Microsoft is also not supporting downgrading as it is not vulnerable, can there be an OS check ?

[RobTho]

https://datatracker.ietf.org/doc/rfc7507/

[Marcel-Balk]

@RobTho
"All unnecessary protocol downgrades are undesirable (e.g., from TLS
1.2 to TLS 1.1,"

TLS1.3 is not considerd in this document, Microsoft is also mentioning that the attack is not present on Windows server enviroments.

"If a client sets ClientHello.client_version to its highest
supported protocol version, it MUST NOT include TLS_FALLBACK_SCSV
in ClientHello.cipher_suites."

  This is the case with Microsoft as the highest protocol is TLS1.3 in this case, SSLLabs should show an A+ because it is following this.

[Marcel-Balk]

Not using TLS1.3 is not OK, the check needs to be adjusted.

[ArchangeGabriel]

See also #815

[Sebazzz]

As far as i know MS do not support "Downgrade attack prevention" but maybe changed with 2022.

From what I gather you are right, this is still not supported with Windows Server 2022.

Still, it does seem backward to have TLS 1.2 result in A+ and TLS 1.3 then result in A.

[Marcel-Balk]

Microsoft has investigated the issue and mention that this is not a problem in Windows server and there fore not needed to build in the feature.

Beacuse of this an A+ is a valid score.

[JordanRieger]

@Marcel-Balk Do you have a link confirming that "Microsoft has investigated the issue and mention that this is not a problem in Windows server"? I can't find any information on that.

[Marcel-Balk]

They reported it in a ticket to us pointing to this document: https://docs.microsoft.com/en-us/security/engineering/solving-tls1-problem

What indeed in "he Current State of Microsoft's TLS 1.0 implementation" describes that they are following protocol, they also mention the only way to do a downgrade is to force on the server and client at the same time, so if you have TLS 1.2 and TLS 1.3 enabled its not a problem.