Parse more of the ClientHello when using SSL3 in the record layer

[BrennanConroy]

Describe the bug

Using the TlsFrameHelper to parse ClientHello doesn't populate very much information if the record layer version is SSL3.0. Specifically, the TlsFrameInfo.SupportedVersions isn't populated with the ClientHello version (which is likely TLS1.2 or higher). This means application level logic can't easily do early SSL/TLS version checks to reject requests.

This is due to the following check

yarp/src/ReverseProxy/Utilities/TlsFrameHelper.cs

Line 325 in 68f81c4

if (((int)info.Header.Version >= (int)SslProtocols.Tls) &&

SSL3.0 is less than TLS1.0 so the rest of the ClientHello parsing is skipped.

From the TLS1.2 Protocol RFC
https://www.rfc-editor.org/rfc/rfc5246#appendix-E

TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use
compatible ClientHello messages; thus, supporting all of them is
relatively easy.

Earlier versions of the TLS specification were not fully clear on
what the record layer version number (TLSPlaintext.version) should
contain when sending ClientHello (i.e., before it is known which
version of the protocol will be employed). Thus, TLS servers
compliant with this specification MUST accept any value {03,XX} as
the record layer version number for ClientHello.
TLS clients that wish to negotiate with older servers MAY send any
value {03,XX} as the record layer version number. Typical values
would be {03,00}

It seems like the check could easily be changed to >= SslProtocols.Ssl3. I did a quick test with this and it looks like it correctly parsed the data and showed Ssl3 | Tls12 in SupportedVersions.

To Reproduce

Send a TLS request with SSL3 as the version in the record layer and TLS1.2 as the ClientHello version.

Further technical details

N/A

[MihaZupan]

cc: @wfurt, @rzikm

I'm assuming this is related to dotnet/runtime#113729, dotnet/aspnetcore#60805?

[wfurt]

I suppose we can do more. There really was no reason to do it and testing is going to be pain IMHO.

[BrennanConroy]

cc: @wfurt, @rzikm

I'm assuming this is related to dotnet/runtime#113729, dotnet/aspnetcore#60805?

Surprisingly no, but it probably would be helpful for those as well. This came from a team who wants to reject connections earlier if the TLS version is too low.

[wfurt]

it it comes as SSL3 frame it it probably already too old :) I never seen that with TLS 1.2+

[crosenblatt]

This scenario popped up for a number of clients using IoT devices. I can share with you more data over Teams if you wish.

[wfurt]

I think getting samples of the Hello should be sufficient. We will need to synthesize tests from that. I'm not sure who will work on that. I'm on loan to other assignments for near future.

[crosenblatt]

I already gave Brennan one - his testing against that led to this issue :)

[aardrasystems]

@crosenblatt @wfurt

We experienced this issue with our Azure Function App, but it has now been resolved on our end.

Our IoT devices send an HTTPS GET request to our API to retrieve data before proceeding with the application logic.

All our devices have SSL and TLS enabled(This is due to our GSM module and keeping the module flexible), though they currently do not support TLS 1.3. We plan to update some of these devices to only use TLS 1.2

Could you please provide more information on the issue and how we can prevent it in the future? Or would I be right in understanding that it has already been resolved?

Also, could you clarify where the fix was applied? I’d like to avoid reintroducing the issue by republishing our Function App. Can this fix be incorporated into my local copy of the Function App or its dependencies?

Another concern I have is regarding IoT Hub and Azure Blob Storage, especially if they are being updated to require a minimum of TLS 1.2. We’d like to avoid any service interruptions there as well.

I’d be happy to connect over Teams if that’s easier to discuss this further.

Looking forward to your response.

[godly]

@aardrasystems
To make your code compatible with the used yarp version (likely no longer in use) you'd need to set the TLS version record to 0x0303 within the ClientHello.

To reproduce this issue you might use the attached code. It is limited to send a ClientHello and not useful for other purposes.

client_hello.py.txt

[aardrasystems]

@godly We are running our API via Azure Function app consumption plan using C# so I don't think its the yarp version.

Our Iot devices all have internal setting that enables SSL, TLS1, TLS1.1 and TLS 1.2.

I believe this has been resolved for our resources, but is this change editable by our actual Visual Studio project?

[godly]

@aardrasystems
For us there were two changes in the cloud / region, one around April 1st and the 2nd around April 15th and we had issues during this time. The used yarp version / app is not directly related the version available here.

I added some comments to the Python code which might help you to understand the issue we experienced.

[aardrasystems]

@godly OK, so am i correct in understanding our IoT device that have enabled all (SSL,TLS1,1.1 and 1.2), should be OK for the future?

Can we get more information on yarp and function app or is this not available?

[BrennanConroy]

Can you two please move this conversation elsewhere? It looks like it has nothing to do with this issue, which is just about surfacing more of the parsed ClientHello if you happen to use the TlsFrameHelper in YARP.