UnsolicitedCertificateTypeExtension is not RFC 7250 compliant #2257
Description
Checklist
- I've searched the issue tracker for similar bugs.
Describe the bug
Consider the following scenario:
- a rustls server using X.509 certificates
- a third party client advertising both X.509 certificates and Raw Public Keys as supported client certificate types
If this client attempts to connect to the rustls server, the handshake will fail with TLS alert "handshake failure" and message "UnsolicitedCertificateTypeExtension".
This is not RFC 7250 compliant.
To Reproduce
Steps to reproduce the behavior:
- Run a rustls server with a X.509 cert and Raw Public Key support disabled
- Craft a ClientHello with a client_certificate_types extension advertising both X.509 and Raw Public Keys (RFC 7250)
- Attempt to connect
Applicable Version(s)
rustls 0.23.16
Expected behavior
The client and server share a supported certificate type (both understand X.509).
According to RFC 7250 Section 4.2, the server should then behave as follows:
- Don't send an alert (RFC 7250 makes no specific allowances to fail if both peers support X.509)
- Respond with the client_certificate_type extension in ServerHello; set the cert type to X.509
- Same for server_certificate_type
Additional context
Here's an example of this failure in the wild. Below is a ClientHello sent by third party software
DEBUG 12-04 20:24:30.682265 1431788 f0 0 src/waltz/tls/fd_tls.c(1013): HEXDUMP "client hello" (194 bytes at 0x7fffe35689b0)
0000: 01 00 00 be 03 03 76 b0 fc 10 9e b7 09 a3 0f 1c ......v.........
0010: 7c 1d 98 8e f6 38 4a ad 12 60 0d e8 75 ce 80 a0 |....8J..`..u...
0020: 54 2f cc 00 44 ea 00 00 02 13 01 01 00 00 93 00 T/..D...........
0030: 2b 00 03 02 03 04 00 33 00 26 00 24 00 1d 00 20 +......3.&.$...
0040: bd c5 6b dd 45 85 c6 e2 a4 f5 aa 02 f9 7f 05 81 ..k.E...........
0050: a5 f4 42 83 3e 7a 73 e1 15 8d 9b 7c 42 ae 6b 31 ..B.>zs....|B.k1
0060: 00 0a 00 04 00 02 00 1d 00 0d 00 04 00 02 08 07 ................
0070: 00 10 00 0d 00 0b 0a 73 6f 6c 61 6e 61 2d 74 70 .......solana-tp
0080: 75 00 39 00 2f 01 02 43 e8 03 02 45 c0 04 08 ff u.9./..C...E....
0090: ff ff ff ff ff ff ff 07 02 44 d0 08 01 00 09 01 .........D......
00a0: 00 0a 01 00 0b 02 40 64 0c 00 0f 08 8e 54 e4 ca ......@d.....T..
00b0: 1f 2e 30 2e 00 14 00 03 02 02 00 00 13 00 03 02 ..0.............
00c0: 02 00 ..
DEBUG 12-04 20:24:30.682831 1431788 f0 0 src/waltz/quic/fd_quic.c(1673): initial pkt_number: 0
WARNING 12-04 20:24:30.682838 1431788 f0 0 src/waltz/quic/fd_quic.c(5524): fd_quic_frame_handle_conn_close_frame - error_code: 296 frame_type: 0 reason: peer is incompatible: UnsolicitedCertificateTypeExtension