Cannot get default_sni to work

1. Environment

1a. Operating system and version

Ubuntu 24.04.3 LTS
x86_64

1b. Caddy version (run `caddy version` or paste commit SHA)

v2.10.2

2. Description

2a. What happens

I am trying to support connections from a Beckhoff TwinCAT 3 IoT HTTPS/REST client, which seemingly does not send SNI.

My assumption was the following option would do the trick:

{
        default_sni imusic.co
}

However, the connection does not succeed:

$ gnutls-cli --disable-sni -p 443 imusic.co
Processed 147 CA certificate(s).
Resolving 'imusic.co:443'...
Connecting to '83.94.121.59:443'...
*** Fatal error: A TLS fatal alert has been received.
*** Received alert [80]: Internal error

2c. Log output

No log entries are seen on the server.

Below is the output from nutls-cli --verbose --debug=9999 --disable-sni -p 443 imusic.co:

|<3>| ASSERT: common.c[_gnutls_x509_get_raw_field2]:1536
|<3>| ASSERT: x509.c[gnutls_x509_crt_get_subject_unique_id]:4029
|<3>| ASSERT: x509.c[gnutls_x509_crt_get_issuer_unique_id]:4076
Processed 147 CA certificate(s).
Resolving 'imusic.co:443'...
Connecting to '83.94.121.59:443'...
|<5>| REC[0xb2d290000]: Allocating epoch #0
|<2>| added 6 protocols, 29 ciphersuites, 22 sig algos and 10 groups into priority list
|<5>| REC[0xb2d290000]: Allocating epoch #1
|<4>| HSK[0xb2d290000]: Adv. version: 3.3
|<2>| Keeping ciphersuite 13.02 (GNUTLS_AES_256_GCM_SHA384)
|<2>| Keeping ciphersuite 13.03 (GNUTLS_CHACHA20_POLY1305_SHA256)
|<2>| Keeping ciphersuite 13.01 (GNUTLS_AES_128_GCM_SHA256)
|<2>| Keeping ciphersuite 13.04 (GNUTLS_AES_128_CCM_SHA256)
|<2>| Keeping ciphersuite c0.2c (GNUTLS_ECDHE_ECDSA_AES_256_GCM_SHA384)
|<2>| Keeping ciphersuite cc.a9 (GNUTLS_ECDHE_ECDSA_CHACHA20_POLY1305)
|<2>| Keeping ciphersuite c0.ad (GNUTLS_ECDHE_ECDSA_AES_256_CCM)
|<2>| Keeping ciphersuite c0.0a (GNUTLS_ECDHE_ECDSA_AES_256_CBC_SHA1)
|<2>| Keeping ciphersuite c0.2b (GNUTLS_ECDHE_ECDSA_AES_128_GCM_SHA256)
|<2>| Keeping ciphersuite c0.ac (GNUTLS_ECDHE_ECDSA_AES_128_CCM)
|<2>| Keeping ciphersuite c0.09 (GNUTLS_ECDHE_ECDSA_AES_128_CBC_SHA1)
|<2>| Keeping ciphersuite c0.30 (GNUTLS_ECDHE_RSA_AES_256_GCM_SHA384)
|<2>| Keeping ciphersuite cc.a8 (GNUTLS_ECDHE_RSA_CHACHA20_POLY1305)
|<2>| Keeping ciphersuite c0.14 (GNUTLS_ECDHE_RSA_AES_256_CBC_SHA1)
|<2>| Keeping ciphersuite c0.2f (GNUTLS_ECDHE_RSA_AES_128_GCM_SHA256)
|<2>| Keeping ciphersuite c0.13 (GNUTLS_ECDHE_RSA_AES_128_CBC_SHA1)
|<2>| Keeping ciphersuite 00.9d (GNUTLS_RSA_AES_256_GCM_SHA384)
|<2>| Keeping ciphersuite c0.9d (GNUTLS_RSA_AES_256_CCM)
|<2>| Keeping ciphersuite 00.35 (GNUTLS_RSA_AES_256_CBC_SHA1)
|<2>| Keeping ciphersuite 00.9c (GNUTLS_RSA_AES_128_GCM_SHA256)
|<2>| Keeping ciphersuite c0.9c (GNUTLS_RSA_AES_128_CCM)
|<2>| Keeping ciphersuite 00.2f (GNUTLS_RSA_AES_128_CBC_SHA1)
|<2>| Keeping ciphersuite 00.9f (GNUTLS_DHE_RSA_AES_256_GCM_SHA384)
|<2>| Keeping ciphersuite cc.aa (GNUTLS_DHE_RSA_CHACHA20_POLY1305)
|<2>| Keeping ciphersuite c0.9f (GNUTLS_DHE_RSA_AES_256_CCM)
|<2>| Keeping ciphersuite 00.39 (GNUTLS_DHE_RSA_AES_256_CBC_SHA1)
|<2>| Keeping ciphersuite 00.9e (GNUTLS_DHE_RSA_AES_128_GCM_SHA256)
|<2>| Keeping ciphersuite c0.9e (GNUTLS_DHE_RSA_AES_128_CCM)
|<2>| Keeping ciphersuite 00.33 (GNUTLS_DHE_RSA_AES_128_CBC_SHA1)
|<4>| EXT[0xb2d290000]: Preparing extension (Server Name Indication/0) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Extended Master Secret/23) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Extended Master Secret/23 (0 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Client Certificate Type/19) for 'client hello'
|<4>| EXT[0xb2d290000]: Client certificate type was set to default cert type (X.509). We therefore do not send this extension.
|<4>| EXT[0xb2d290000]: Preparing extension (PSK Key Exchange Modes/45) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension PSK Key Exchange Modes/45 (3 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Maximum Record Size/1) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Supported EC Point Formats/11) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Supported EC Point Formats/11 (2 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Record Size Limit/28) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Record Size Limit/28 (2 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Supported Groups/10) for 'client hello'
|<4>| EXT[0xb2d290000]: Sent group SECP256R1 (0x17)
|<4>| EXT[0xb2d290000]: Sent group SECP384R1 (0x18)
|<4>| EXT[0xb2d290000]: Sent group SECP521R1 (0x19)
|<4>| EXT[0xb2d290000]: Sent group X25519 (0x1d)
|<4>| EXT[0xb2d290000]: Sent group X448 (0x1e)
|<4>| EXT[0xb2d290000]: Sent group FFDHE2048 (0x100)
|<4>| EXT[0xb2d290000]: Sent group FFDHE3072 (0x101)
|<4>| EXT[0xb2d290000]: Sent group FFDHE4096 (0x102)
|<4>| EXT[0xb2d290000]: Sent group FFDHE6144 (0x103)
|<4>| EXT[0xb2d290000]: Sent group FFDHE8192 (0x104)
|<4>| EXT[0xb2d290000]: Sending extension Supported Groups/10 (22 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Signature Algorithms/13) for 'client hello'
|<4>| EXT[0xb2d290000]: sent signature algo (9.4) ML-DSA-44
|<4>| EXT[0xb2d290000]: sent signature algo (9.5) ML-DSA-65
|<4>| EXT[0xb2d290000]: sent signature algo (9.6) ML-DSA-87
|<4>| EXT[0xb2d290000]: sent signature algo (4.1) RSA-SHA256
|<4>| EXT[0xb2d290000]: sent signature algo (8.9) RSA-PSS-SHA256
|<4>| EXT[0xb2d290000]: sent signature algo (8.4) RSA-PSS-RSAE-SHA256
|<4>| EXT[0xb2d290000]: sent signature algo (4.3) ECDSA-SHA256
|<4>| EXT[0xb2d290000]: sent signature algo (8.7) EdDSA-Ed25519
|<4>| EXT[0xb2d290000]: sent signature algo (5.1) RSA-SHA384
|<4>| EXT[0xb2d290000]: sent signature algo (8.10) RSA-PSS-SHA384
|<4>| EXT[0xb2d290000]: sent signature algo (8.5) RSA-PSS-RSAE-SHA384
|<4>| EXT[0xb2d290000]: sent signature algo (5.3) ECDSA-SHA384
|<4>| EXT[0xb2d290000]: sent signature algo (8.8) EdDSA-Ed448
|<4>| EXT[0xb2d290000]: sent signature algo (6.1) RSA-SHA512
|<4>| EXT[0xb2d290000]: sent signature algo (8.11) RSA-PSS-SHA512
|<4>| EXT[0xb2d290000]: sent signature algo (8.6) RSA-PSS-RSAE-SHA512
|<4>| EXT[0xb2d290000]: sent signature algo (6.3) ECDSA-SHA512
|<4>| EXT[0xb2d290000]: sent signature algo (2.1) RSA-SHA1
|<4>| EXT[0xb2d290000]: sent signature algo (2.3) ECDSA-SHA1
|<4>| EXT[0xb2d290000]: Sending extension Signature Algorithms/13 (40 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Supported Versions/43) for 'client hello'
|<2>| Advertizing version 3.4
|<2>| Advertizing version 3.3
|<2>| Advertizing version 3.2
|<2>| Advertizing version 3.1
|<4>| EXT[0xb2d290000]: Sending extension Supported Versions/43 (9 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Session Ticket/35) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Session Ticket/35 (0 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (ALPN/16) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (OCSP Status Request/5) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension OCSP Status Request/5 (5 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Post Handshake Auth/49) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Compress Certificate/27) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Safe Renegotiation/65281) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Safe Renegotiation/65281 (1 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (SRTP/14) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Cookie/44) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Encrypt-then-MAC/22) for 'client hello'
|<4>| EXT[0xb2d290000]: Sending extension Encrypt-then-MAC/22 (0 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Server Certificate Type/20) for 'client hello'
|<4>| EXT[0xb2d290000]: Server certificate type was set to default cert type (X.509). We therefore do not send this extension.
|<4>| EXT[0xb2d290000]: Preparing extension (Key Share/51) for 'client hello'
|<4>| EXT[0xb2d290000]: sending key share for SECP256R1
|<4>| EXT[0xb2d290000]: sending key share for X25519
|<4>| EXT[0xb2d290000]: Sending extension Key Share/51 (107 bytes)
|<4>| EXT[0xb2d290000]: Preparing extension (Early Data/42) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (ClientHello Padding/21) for 'client hello'
|<4>| EXT[0xb2d290000]: Preparing extension (Pre Shared Key/41) for 'client hello'
|<4>| HSK[0xb2d290000]: CLIENT HELLO was queued [374 bytes]
|<11>| HWRITE: enqueued [CLIENT HELLO] 374. Total 374 bytes.
|<11>| HWRITE FLUSH: 374 bytes in buffer.
|<5>| REC[0xb2d290000]: Preparing Packet Handshake(22) with length: 374 and min pad: 0
|<9>| ENC[0xb2d290000]: cipher: NULL, MAC: MAC-NULL, Epoch: 0
|<11>| WRITE: enqueued 379 bytes for 0x5. Total 379 bytes.
|<5>| REC[0xb2d290000]: Sent Packet[1] Handshake(22) in epoch 0 and length: 379
|<11>| HWRITE: wrote 1 bytes, 0 bytes left.
|<11>| WRITE FLUSH: 379 bytes in buffer.
|<11>| WRITE: wrote 379 bytes, 0 bytes left.
|<3>| ASSERT: buffers.c[get_last_packet]:1139
|<10>| READ: Got 5 bytes from 0x5
|<10>| READ: read 5 bytes from 0x5
|<10>| RB: Have 0 bytes into buffer. Adding 5 bytes.
|<10>| RB: Requested 5 bytes
|<5>| REC[0xb2d290000]: SSL 3.3 Alert packet received. Epoch 0, length: 2
|<5>| REC[0xb2d290000]: Expected Packet Handshake(22)
|<5>| REC[0xb2d290000]: Received Packet Alert(21) with length: 2
|<10>| READ: Got 2 bytes from 0x5
|<10>| READ: read 2 bytes from 0x5
|<10>| RB: Have 5 bytes into buffer. Adding 2 bytes.
|<10>| RB: Requested 7 bytes
|<5>| REC[0xb2d290000]: Decrypted Packet[0] Alert(21) with length: 2
|<5>| REC[0xb2d290000]: Alert[2|80] - Internal error - was received
|<3>| ASSERT: record.c[record_add_to_buffers]:887
|<3>| ASSERT: record.c[record_add_to_buffers]:894
|<3>| ASSERT: record.c[_gnutls_recv_in_buffers]:1565
|<3>| ASSERT: buffers.c[_gnutls_handshake_io_recv_int]:1412
|<3>| ASSERT: handshake.c[_gnutls_recv_handshake]:1613
|<3>| ASSERT: handshake.c[handshake_client]:3104
|<13>| BUF[HSK]: Emptied buffer
*** Fatal error: A TLS fatal alert has been received.
*** Received alert [80]: Internal error
|<3>| ASSERT: alert.c[gnutls_alert_send_appropriate]:382

2d. Workaround(s)

Not aware of any.

2e. Relevant links

Live domain that exhibits the issue: imusic.co

https://testtls.com/imusic.co/443 reports failure for requests w/o SNI:

3. Tutorial (minimal steps to reproduce the bug)

Create a config with a public domain and default_sni:

{
        default_sni example.com
}

example.com {
        root * /srv/path/public
        encode
        file_server
}

Let Caddy obtain a SSL certificate for the domain
Verify that normal TLS connections (with SNI) work:

gnutls-cli -p 443 example.com
...
- Handshake was completed

Observe that TLS connections without SNI fail with a TLS fatal alert:

gnutls-cli --disable-sni -p 443 example.com
Processed 147 CA certificate(s).
Resolving 'example.com:443'...
Connecting to '1.2.3.4:443'...
*** Fatal error: A TLS fatal alert has been received.
*** Received alert [80]: Internal error

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Cannot get `default_sni` to work #7325

1. Environment

1a. Operating system and version

1b. Caddy version (run `caddy version` or paste commit SHA)

2. Description

2a. What happens

2c. Log output

2d. Workaround(s)

2e. Relevant links

3. Tutorial (minimal steps to reproduce the bug)

Assistance Disclosure

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Uh oh!

Cannot get default_sni to work #7325

Description

1. Environment

1a. Operating system and version

1b. Caddy version (run caddy version or paste commit SHA)

2. Description

2a. What happens

2c. Log output

2d. Workaround(s)

2e. Relevant links

3. Tutorial (minimal steps to reproduce the bug)

Assistance Disclosure

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Cannot get `default_sni` to work #7325

1b. Caddy version (run `caddy version` or paste commit SHA)