"Interoperability failure - 200 Type set to ASCII." because of directory listing parser switch and connection exception

[pkramme]

Describe the bug
When using FTPS to connect to a server, cyberduck is trying out different parsers for getting directory contents.

The LIST -a parser creates a PASV connection, and then tries to connect to the server by using TLS for the IP address, which fails because the server does not have any certificate for just the IP address. This causes Cyberduck to switch to the next parser. Cyberduck then gets confused in the control connection because the server still answers with the following to the previous LIST -a attempt:

226 Closing data connection, sent 0 bytes

Cyberduck interprets this as the response to the next command by the next list parser (CWD /whatever). Finally, the connection fails because the responses do not make sense to Cyberduck.

2026-03-17 12:03:58,439 [Thread-90] INFO  audit.transcript - CWD /import
2026-03-17 12:03:58,454 [Thread-90] INFO  audit.transcript - 250 Directory changed to /import
2026-03-17 12:03:58,454 [Thread-90] INFO  audit.transcript - TYPE A
2026-03-17 12:03:58,468 [Thread-90] INFO  audit.transcript - 200 Type set to ASCII
2026-03-17 12:03:58,468 [Thread-90] INFO  audit.transcript - PASV
2026-03-17 12:03:58,482 [Thread-90] INFO  audit.transcript - 227 Entering Passive Mode (xxx,xxx,xxx,xxx,27,158)
2026-03-17 12:03:58,483 [Thread-90] DEBUG ch.cyberduck.core.ssl.CustomTrustSSLProtocolSocketFactory - Configure SSL parameters with protocols [TLSv1.2, TLSv1.1, TLSv1]
2026-03-17 12:03:58,483 [Thread-90] INFO  ch.cyberduck.core.ssl.CustomTrustSSLProtocolSocketFactory - Enabled cipher suites [...]
2026-03-17 12:03:58,483 [Thread-90] DEBUG ch.cyberduck.core.ssl.CustomTrustSSLProtocolSocketFactory - Handshake for socket SSLSocket[hostname=null, port=0, Session(1773745438482|SSL_NULL_WITH_NULL_NULL)]
2026-03-17 12:03:58,498 [Thread-90] INFO  audit.transcript - LIST -a
2026-03-17 12:03:58,513 [Thread-90] INFO  audit.transcript - 150 Opening ASCII mode data connection for file list
2026-03-17 12:03:58,513 [Thread-90] WARN  ch.cyberduck.core.ftp.FTPClient - SSL session Session(1773745435274|TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256) for socket SSLSocket[hostname=xxx.xxx.xxx.xxx, port=7070, Session(1773745438482|SSL_NULL_WITH_NULL_NULL)] is not rejoinable
2026-03-17 12:03:58,529 [Thread-90] WARN  ch.cyberduck.core.ftp.FTPExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-17 12:03:58,530 [Thread-90] WARN  ch.cyberduck.core.DefaultIOExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-17 12:03:58,530 [Thread-90] WARN  ch.cyberduck.core.ssl.SSLExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-17 12:03:58,530 [Thread-90] WARN  ch.cyberduck.core.ftp.DataConnectionActionExecutor - Server denied data socket operation with Interoperability failure
2026-03-17 12:03:58,530 [Thread-90] WARN  ch.cyberduck.core.ftp.list.FTPListService - Remove Command{command=LIST, arg='-a'} from listing strategies
2026-03-17 12:03:58,530 [Thread-90] INFO  audit.transcript - CWD /import
2026-03-17 12:03:58,531 [Thread-90] INFO  audit.transcript - 226 Closing data connection, sent 0 bytes
2026-03-17 12:03:58,531 [Thread-90] INFO  audit.transcript - TYPE A
2026-03-17 12:03:58,545 [Thread-90] INFO  audit.transcript - 250 Directory changed to /import
2026-03-17 12:03:58,545 [Thread-90] INFO  audit.transcript - PASV
2026-03-17 12:03:58,559 [Thread-90] INFO  audit.transcript - 200 Type set to ASCII

2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > CWD /import
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 250 Directory changed to /import
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > TYPE A
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 200 Type set to ASCII
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > PASV
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 227 Entering Passive Mode (xxx,xxx,xxx,xxx,27,158)
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > LIST -a
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 150 Opening ASCII mode data connection for file list
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 226 Closing data connection, sent 0 bytes
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > CWD /import
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 250 Directory changed to /import
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > TYPE A
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 200 Type set to ASCII
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb > PASV
2026/03/17 12:03:58 60a16bbc8b1135ac6eeb < 227 Entering Passive Mode (xxx,xxx,xxx,xxx,27,171)
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb > CWD /import
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb < 250 Directory changed to /import
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb > TYPE A
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb < 200 Type set to ASCII
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb > PASV
2026/03/17 12:03:59 60a16bbc8b1135ac6eeb < 227 Entering Passive Mode (xxx,xxx,xxx,xxx,30,120)

To Reproduce
Steps to reproduce the behavior:

1. Use FTPS server with certificate for a domain. The server must have incompatible output for the STAT command, so that Cyberduck switches to LIST -a. Ideally, the server responds with compatible output to the STAT for populated directories, but not for empty directories.
2. Connect to the server, and wait for Cyberduck to respond with "Interoperability failure - 200 Type set to ASCII. Please contact your web hosting service provider for assistance."

Expected behavior
Work correctly.

Screenshots

Desktop (please complete the following information):

• OS: MacOS
• Version 26.3.1

Log Files
Included above.

Additional context

[pkramme]

This issue is also the most likely reason why Cyberduck does not work with Minio's FTPS.

[dkocher]

Relates to #10138.

[dkocher]

@pkramme It would be great if you could confirm the fix with build 9.5.0.44562 or later available on Beta now and Snapshot Builds later today as I lack a test environment with the setup you describe.

[pkramme]

I am now getting

Connection failed (xxxyyy)
Internal error. (internal_error) Received fatal alert: internal_error. The connection attempt was rejected. The server may be down, or your network may not be properly configured.

The failure occurs because the server doesn't serve a certificate for the IP address - so this issue has been solved. Thank you!

[dkocher]

I am now getting

Connection failed (xxxyyy)
Internal error. (internal_error) Received fatal alert: internal_error. The connection attempt was rejected. The server may be down, or your network may not be properly configured.

The failure occurs because the server doesn't serve a certificate for the IP address - so this issue has been solved. Thank you!

Can you confirm the pending response from the server after the TLS connection failure is read as expected.

[pkramme]

2026-03-18 10:50:53,777 [Thread-88] INFO  audit.transcript - LIST -a
2026-03-18 10:50:53,792 [Thread-88] INFO  audit.transcript - 150 Opening ASCII mode data connection for file list
2026-03-18 10:50:53,792 [Thread-88] WARN  ch.cyberduck.core.ftp.FTPClient - SSL session Session(1773827453237|TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256) for socket SSLSocket[hostname=xxx.xxx.xxx.xxx, port=7810, Session(1773827453762|SSL_NULL_WITH_NULL_NULL)] is not rejoinable
2026-03-18 10:50:53,807 [Thread-88] WARN  ch.cyberduck.core.ftp.FTPExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-18 10:50:53,808 [Thread-88] WARN  ch.cyberduck.core.DefaultIOExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-18 10:50:53,808 [Thread-88] WARN  ch.cyberduck.core.ssl.SSLExceptionMappingService - Map failure javax.net.ssl.SSLException: (internal_error) Received fatal alert: internal_error
2026-03-18 10:50:53,808 [Thread-88] WARN  ch.cyberduck.core.ftp.DataConnectionActionExecutor - I/O error opening data socket Connection failed
2026-03-18 10:50:53,808 [Thread-88] INFO  audit.transcript - 226 Closing data connection, sent 0 bytes
2026-03-18 10:50:53,808 [Thread-88] DEBUG ch.cyberduck.core.threading.DefaultFailureDiagnostics - Determine cause for failure Connection failed

It's correctly read. After that the connection is terminated and the above error is shown. Pressing "Try again" is then causing Cyberduck to correctly reconnect to the server.