SFTP connection issue

Question

SFTP connection issue

Jonathan 380

Hi，

On Filezilla I created a new site and put 22 as the port to link to SFTP server (using server 2022) why got this issue?

Status: Connection attempt failed with "ECONNREFUSED - Connection refused by server" Error: File transfer failed Error: Got read socket error: ECONNABORTED Error: File transfer failed after transferring 1,898,971,136 bytes in 89 seconds

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2 answers

Your answer

Answer 1

Chen Tran 13,030 Independent Advisor

Hello Jonathan,

Thank you for posting question on Microsoft Windows Forum!

Based on the issue description as well as the provided error message. Well! The issue is not that you configured FileZilla wrong. It might be that the connection abruptly died during a heavy transfer (ECONNABORTED), and when FileZilla automatically tried to reconnect, the server actively rejected it (ECONNREFUSED).

Since Windows Server 2022 uses the built-in OpenSSH server for SFTP. Sometimes, transferring large files at high speeds can cause the sshd (OpenSSH) service to crash or hang. When FileZilla tried to reconnect, the service was no longer listening, resulting in ECONNREFUSED. The suggestion is to log into your Windows Server 2022 machine, open Services (services.msc), and look for OpenSSH SSH Server. If it says "Stopped," start it. In case it says "Running," right-click and restart it. For more information https://learn.microsoft.com/nb-no/windows-server/administration/openssh/openssh_install_firstuse

If the connection dropped exactly at that file size, the server might have forcibly closed the connection because it could not write any more data. Try to check the destination drive on the server. Make sure it is not completely full, and verify that there are no user storage quotas applied to the Windows account you are using for SFTP. On the other hand, since SFTP transfers everything over a single connection. During very fast, large file transfers, the client and server sometimes fail to exchange "keep-alive" messages because the channel is saturated with file data. The server assumes you dropped off and severs the connection. The suggestion here is to extend FileZilla timeout settings. In FileZilla, navigate to Edit > Settings > Connection. Increase the Timeout setting from the default (20 seconds) to 60 or 120 seconds.

Another point worth mentioning here is that many enterprise firewalls, antivirus programs, or cloud security groups monitor traffic. If they see a massive, continuous stream of encrypted data (almost 2GB in 89 seconds is ~21 MB/s), they may classify it as a data exfiltration attack and aggressively kill the connection. Worse, they may temporarily ban your IP address, causing the immediate ECONNREFUSED on the reconnect attempt. It is worth checking the firewall logs on the server or your network's perimeter firewall. You may need to whitelist your IP address or create an exception for large SFTP transfers.

Hope the response provided some helpful insight. If you find this answer useful, please feel free to hit “Accept Answer” so I know it addressed your concern.

Chen Tran 13,030 Reputation points Independent Advisor

2026-09-16T02:22:04.82+00:00

Hi Jonathan,

Hope you are doing well!

May I know the latest status of the query?

Hope the provided information is helpful! If it is. It is appreciated to consider clicking "Accept Answer".
Jonathan 380 Reputation points

2026-09-16T02:25:35.6566667+00:00

In FilZilla, I have 0 timeout (to disable that). Client Pc is having enough space.

Does it mean I can restart OpenSSH service on the server when the issue appears?
Chen Tran 13,030 Reputation points Independent Advisor

2026-09-16T02:41:11.47+00:00

Hi Jonathan,

Thank you for the extra information!

Yes! Restarting the OpenSSH SSH Server (sshd) service on your Windows Server 2022 machine is the correct immediate action to take when that ECONNREFUSED error appears. It will get the service listening on port 22 again so you can reconnect.

Another point worth mentioning here is to check the Event Viewer on your Windows Server 2022 machine immediately after it crashes by navigating to Applications and Services Logs > OpenSSH > Operational (or Admin). Look for critical errors or warnings that occurred at the exact time the transfer dropped. It will usually tell you if it was an out-of-memory exception, a buffer issue, or a disk write error.

Also, the built-in OpenSSH feature-on-demand version that ships with Windows Server 2022 can sometimes lag behind the latest stable releases, occasionally leading to memory leaks or buffer crashes during high-speed, multi-gigabyte transfers. If the Event Viewer shows the sshd.exe process is faulting, you may want to update to the latest release of OpenSSH for Windows.

Hope the provided information is helpful! If it is. It is appreciated to consider clicking "Accept Answer".
Jonathan 380 Reputation points

2026-09-16T02:56:18.6466667+00:00

Thanks a lot.

OpenSSH Auth. agent needs to be started (enabled)?

The same client was fine ever to download the same from Server 2025.
Chen Tran 13,030 Reputation points Independent Advisor

2026-09-16T03:12:20.9066667+00:00
Hi Jonathan,

Regarding your latest query. Well! In fact, the OpenSSH Authentication Agent (ssh-agent) does not need to be started for standard password-based SFTP connections or basic key-based authentication. Its primary job is to hold private keys in memory so you do not have to re-enter passphrase credentials repeatedly during local SSH operations. It is not required for the OpenSSH SSH Server service (sshd) to accept inbound SFTP connections.

For further reference.

https://learn.microsoft.com/en-us/windows-server/administration/openssh/openssh-overview

Hope the above information is helpful!
Chen Tran 13,030 Reputation points Independent Advisor

2026-09-17T01:29:03.5833333+00:00

Hi Jonathan,

Hope you are doing well!

May I know the latest status of the query?

Hope the response provided some helpful insight. If you find this answer useful, remember “Accept Answer” so I know it addressed your concern.
Jonathan 380 Reputation points

2026-09-17T02:07:48.9+00:00

Hi Tran,

I tried to restart OpenSSH server service when doing the download. But it is not a good way for that and is there any root resolution?

Using the same client PC I was ever fine to get the download (same file) well from another Server 2025 machine.
Jonathan 380 Reputation points

2026-09-17T10:03:42.9466667+00:00

Any help?
Chen Tran 13,030 Reputation points Independent Advisor

2026-09-17T11:20:36.9733333+00:00

Hi Jonathan,

Based on the best available information as well as the extra research. The plausible explanation to this hehavior is that Windows Server 2022 ships by default with an older build of Win32-OpenSSH (often version v8.1.x or v8.6.x) via the optional Windows Features list. There are some reports of memory leak and heap-buffer during high-throughput, multi-gigabyte SFTP stream operations, causing sshd.exe to crash silently mid-transfer. While Windows Server 2025 includes a significantly newer, stabilized OpenSSH release out of the box.

It is worth checking the exact reason sshd died on Server 2022 by opening Event Viewer on the Server 2022 machine. Navigate to Windows Logs > Application. Look for Event ID 1000 (Application Error) at the exact time the connection died. If Faulting application name: sshd.exe is present with a module crash like ntdll.dll or bcrypt.dll. Then you can consider to update OpenSSH to the latest version.

Hope the above response provides some helpful insight!
Jonathan 380 Reputation points

2026-09-18T03:59:25.6466667+00:00

Thanks a lot.

Look for Event ID 1000 (Application Error) at the exact time the connection died. If Faulting application name: sshd.exe is present with a module crash like ntdll.dll or bcrypt.dll. Then you can consider to update OpenSSH to the latest version.

Before seeing that in Event viewer, can we also do the update on Open SSH within server 22?

Answer 2

For an SFTP connection to a Windows Server 2022 host, ECONNREFUSED - Connection refused by server usually means the server is not accepting the connection on the target port.

Use this checklist:

Verify the server is using SFTP, not FTP/FTPS.
- In FileZilla, the protocol must be SFTP - SSH File Transfer Protocol.
- SFTP normally uses port 22.
Confirm the OpenSSH Server service is running on Windows Server.
- If the OpenSSH Server service does not start, or SFTP connections hang, validate the configuration with:
```
     sshd -t
```
- Also review Event Viewer for related events.
Check the OpenSSH configuration.
- In sshd_config, make sure the following entry is present and correctly formatted:
```
     Subsystem sftp sftp-server.exe
```
- Make sure there are no trailing spaces or invalid entries in sshd_config.

Restart the OpenSSH Server service after any config change.

   NET STOP "OpenSSH SSH Server" && NET START "OpenSSH SSH Server"

Enable SFTP logging to capture the refusal cause.
- Edit %ProgramData%\ssh\sshd_config
- Set:
```
     SyslogFacility LOCAL0
     LogLevel DEBUG3
```
- Add or update:
```
     Subsystem sftp sftp-server.exe -f LOCAL0 -l DEBUG3
```
- Restart the service.
- Then review logs in %ProgramData%\ssh\logs.
If authentication is failing after connection starts, check key and permission settings.
- For key-based auth, store admin keys in C:\ProgramData\ssh\administrators_authorized_keys and verify permissions.
- If the server refuses the key, add:
```
     PubkeyAcceptedKeyTypes +ssh-rsa
     HostKeyAlgorithms +ssh-rsa
```
- Restart the OpenSSH Server service after making the change.
If transfers start and then abort, check permissions on the SFTP directories.
- Make sure ChrootDirectory points to a local directory, not a UNC path.
- Make sure SYSTEM/Administrators owns the chroot directory.
- Make sure each user has a writable directory inside the chroot, but does not have write permission on the chroot directory itself.
- Use icacls in an elevated Command Prompt to verify and repair NTFS permissions.

The ECONNABORTED after transferring part of the file suggests the connection was established and then dropped during transfer. In that case, the most relevant checks are:

OpenSSH service health
sshd_config validity
SFTP subsystem entry
Event Viewer
SFTP logging
NTFS/chroot permissions