Brian Goodkin (Customer) asked a question.
We are observing an interoperability issue between WS_FTP Server and a recent SFTP client release that enforces stricter protocol validation.
Summary
During SFTP v3 sessions, WS_FTP Server returns attribute flags with values that include bits not defined in the protocol (e.g., 0x3C). FileZilla 3.70.5 treats this as a protocol error and fails directory listing operations. (Reference: SFTP v3 draft specification – https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-02)
Environment observed
- WS_FTP Server: 8.8.3.63 & 10.0.1.43
- Protocol: SFTP (SSH-2.0-WS_FTP-SSH_x.x.x.x)
Behavior
- FileZilla 3.70.4 and prior: Works (ignores unknown bits)
- FileZilla 3.70.5: Fails with
Cannot parse attributes, unknown bits set in flags: 60
- Other clients tested (WinSCP, Bitvise, and integration platforms) continue to function normally
Context
This appears to be long-standing server behavior that was previously tolerated by some clients and is now surfaced due to stricter validation in FileZilla 3.70.5.
No immediate action or response is required on this thread. The intent is simply to document the behavior for awareness.
This is also happening with 10.0.2.54 and 8.6.1.2711
FillaZilla developer, Tim Kosse, seems to be calling this a WS_FTP bug: #13392 (Error When Connecting with Version 3.70.5) – FileZilla
"This is a server-side bug that is to be treated as a protocol error according to the specifications. Please contact your server vendor for further assistance."
any update on this? We are experiencing same thing. being told it's an issue with the server complying with the standard flags values.
We are experiencing the same issue.. please give an update on this.
The FileZilla Developer made a note on the bug report in my previous post giving a full explanation of why the change was made and why it is recommended that WS_FTP work on correcting this issue. They also made the concession that they will have added the ability to ignore unknown flags starting with the 2026-05-21 nightly build (FileZilla - Nightly Builds), so at least there is a work around for people who use filezilla, though it hasn't yet shown up in the full release. I've tested the nightly build and it works as expected.
Same issue here. Just updated to latest wsftp edition 10.0.2 hoping it would resolve the issue, but same issue with filezilla 3.70.5 release.
Someone posted a WS_FTP 10.0.2 patch in the FileZilla bug report. I was able to get the same dlls from Progress support for 10.0.2
hi there. @* IT Support (Customer) so will there be files to download or a patched release or do we all have to open a supportticket to get the proper dlls for version 10.0.2?
This issue has been resolved in the latest WS_FTP Server release, 10.0.3.