TLS_FALLBACK_SCSV fails on hiawatha-webserver.org

[ivanr]

Hugo reported the problem:

"Since the SSL Labs grading change, I noticed that SSL Labs says my webserver doesn’t support TLS_FALLBACK_SCSV. It did say so before. I use the Hiawatha webserver which uses mbed TLS. mbed TLS has SCSV support. Can you tell me what’s going on?"

Source: https://blog.qualys.com/ssllabs/2016/11/16/announcing-ssl-labs-grading-changes-for-2017#comment-112341

FYI: The tool https://github.com/rbsec/sslscan says my webserver supports SCSV.

[bhushan5640]

Yes test using openssl also shows support for SCSV. We will resolve it soon. Thanks for reporting.

[bhushan5640]

There are no changes in SCSV fallback test on SSL Labs.

I observed the following behavior: when TLS_FALLBACK_SCSV is sent at the end of the list, Server correctly sends fallback alert but not when it is not last one.

Case 1: Client should send TLS_FALLBACK_SCSV at the end of ciphers it intends to negotiate. SSL Labs send it at the end but before the TLS_EMPTY_RENEGOTIATION_INFO_SCSV

Here server should send the fallback alert and reject handshake as described here, but it does not.

Case 2: When TLS_FALLBACK_SCSV is sent at the end of the all ciphers, Server behaves correctly with fallback alert

Tools which send Fallback scsv at the very end reports positive. But It seems issue on the Server end, It doesn't behave correctly in all cases.

I have notified the mbed TLS developer.

Submitted an issue to the mbed TLS development team.

There was indeed a bug in mbed TLS, which has been fixed. This issue can be closed. Thanks for the help!