• Registered: 2024-02-01
  • Posts: 6

Topic: wolfSSL does not interpret Alert correctly during handshake

During the handshake, wolfSSL will not interpret an Alert message (decimal 15) correctly coming back from the server, and the error message it reports is assuming to decoding a ServerHello rather than Alert.

This happens for example when SNI is required but was not enabled by the wolfSSL client, the server responds with an Alert. wolfSSL then wrongly starts interpreting the 5 bytes as if it where a ServerHello, failing to read the actual Alert error codes itself (requiring to read a few extra bytes).

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  • Registered: 2015-10-07
  • Posts: 423

Re: wolfSSL does not interpret Alert correctly during handshake

Hi Leon,

Thank you for this report. Can you provide a Wireshark track of this and steps to reproduce? Does this happen with both TLS v1.2 and TLS v1.3?

Please confirm the wolfSSL client version you are using and which TLS server (if possible). It is also nice to get the logs with --enable-debug (DEBUG_WOLFSSL) and calling wolfSSL_Debugging_ON();.

Can you tell us a bit about your project and where you are located?

Thanks,
David Garske, wolfSSL

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3 Reply by likewise (edited by likewise 2024-06-05 00:21:14)

  • Registered: 2024-02-01
  • Posts: 6

Re: wolfSSL does not interpret Alert correctly during handshake

Not an answer to all your questions, but this is the output that my finding are based on. I might be able to share more details in a PM.

I used MSG_PEEK on the socket, to inspect the 7 received bytes, which are an Alert message rather than a ServerHello.

connect() == EINPROGRESS: Operation now in progress
epoll() EPOLLOUT: TCP socket connected.
my_IOSend() send(len=238)=238
TX: 16 03 03 00 e9 01 00 00 e5 03 03 e0 7b 69 d7 97 7c 9b c5 11 47 ce 09 b4 7a 24 68 52 8b 14 c0 9a 09 45 b3 51 8f 41 89 34 fb fa 9f 00 00 6a c0 2c c0 2b c0 30 c0 2f 00 9f 00 9e 00 ab 00 34 00 a7 00 aa cc a9 cc a8 cc aa c0 27 c0 23 c0 28 c0 24 c0 0a c0 09 c0 07 c0 08 c0 14 c0 13 c0 11 c0 12 c0 ac c0 ae c0 af 00 6b 00 67 00 39 00 33 00 16 cc 14 cc 13 cc 15 c0 06 00 b3 00 b2 c0 a6 c0 a7 cc ab cc ac cc ad c0 37 d0 01 00 b5 c0 3a 00 b4 00 45 00 88 00 be 00 c4 01 00 00 52 00 0d 00 20 00 1e 06 03 05 03 04 03 08 07 08 08 08 06 08 0b 08 05 08 0a 08 04 08 09 06 01 05 01 04 01 03 01 00 0b 00 02 01 00 00 0a 00 1c 00 1a 00 19 00 1c 00 18 00 1b 00 1e 00 17 00 16 00 1a 00 1d 00 15 00 14 01 01 01 00 00 16 00 00 00 17 00 00  (238)
nevent #1/1 has 2 events: OUT IN
available == 7
RX: 15 03 01 00 02 02 28 (7/7) PEEK
AlertProtocol (==21==0x15)
AlertLevel: 2
AlertDescription: 40 handshake_failure
my_IORecv() recv(len=5) = 5
15 03 01 00 02
my_IOSend() send(len=7)=7
TX: 15 03 03 00 02 02 46  (7)
Failed to connect wolfSSL_connect()=-1, wolfSSL_get_error(ssl, -1) = -326 (record layer version error)

Testing against the same (public) server with OpenSSL gave, which is correct:

807B8AF7FF7F0000:error:0A000410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure:../ssl/record/rec_layer_s3.c:1586:SSL alert number 40

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  • Registered: 2015-10-07
  • Posts: 423

Re: wolfSSL does not interpret Alert correctly during handshake

Hi Leon,

I've transferred this incident to our internal Zendesk system. This will enable a better channel for communicating the details to help us reproduce and fix.

Thanks,
David Garske, wolfSSL

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