Hi Martin,

I will be taking over this Problem from cpanne. I've Tested all Versions you sent and the error is still the same. I have added all the Logs in a .zip.

Thank you for your help.

Thanks. I've emailed you few more builds to test.

Hi Martin,

I testet both of the build versions. The Error is still the same on both of them. I Added the Logs in a .zip.

Thank you for your help.

@cpanne: I have sent you an email.

martin wrote:

Ok, then it might be due to OpenSSL 3 and its more strict security. Try this:

sessionOptions.AddRawSettings("MinTlsVersion", "10");

(Decreasing min TLS version has a side effect of decreasing security level even for newer protocol versions)

Hi Martin this didn't helped I also tried the Max TLS Setting to see if it works with TLS 11 and lower but then it just stops.

I'm not sure but my idea is that somehow Windows handles Tasks different when they are executed in the Background as a Service maybe the tasks are getting throttled down or something like that but if that is true why is it working in 6.1.2!? And why is it working on a different System with the same OS version and configured to use the same Proxy as the other Server?

I added the logs of my tests in a zip.

Hi @cpanne,

thanks for the detailed explanation. A couple of thoughts that might help narrow this down:

1. **Local System vs. User account**
   
   
   
   • The SYSTEM account usually has very restricted network/proxy configuration compared to a normal user account. For example, proxy settings (WinHTTP vs. WinINET) are per-user and SYSTEM often has none configured. That could explain why it works interactively, but not as a service.
     
   • You can check the WinHTTP proxy settings for `SYSTEM` with:
     

     netsh winhttp show proxy

     
     and, if needed, copy your user’s proxy config:
     

     netsh winhttp import proxy source=ie

     
     
   
   
   
2. **Differences between versions (6.1.2.0 vs. 6.5.3.0)**
   
   
   
   • In newer builds, WinSCP’s WebDAV implementation may rely more heavily on proper proxy settings. That could expose the missing proxy config for SYSTEM.
     
   • Double-check release notes for WebDAV changes around 6.5.x.
     
   
   
   
3. **Diagnostics**
   
   
   
   • Try running the same code with `Logging enabled` at a higher verbosity (Session.DebugLogPath). That may show whether the service is stuck at proxy negotiation.
     
   • Also test the service under a dedicated service account (instead of SYSTEM) that has the correct proxy configuration.
     
   
   
   
4. **Workarounds to try**
   
   
   
   • Configure proxy for SYSTEM as shown above.
     
   • Run the service under a domain/user account instead of SYSTEM.
     
   • If your environment allows, bypass the proxy for Nextcloud’s host to confirm the proxy is the bottleneck.
     
   
   

So in short: the difference is most likely due to SYSTEM having no proxy config, and the newer WinSCP/WebDAV version depending on it.

Hope this helps — let us know if updating the SYSTEM proxy settings resolves the issue.

Ok, then it might be due to OpenSSL 3 and its more strict security. Try this:

(Decreasing min TLS version has a side effect of decreasing security level even for newer protocol versions)

Hi Martin,
It is very Important to know that I can't test it with using the UI because then the Problem isn't there. The problem is only there when The Process is getting Executet as a Service with the User SYSTEM. When i start the UI or execute our Program as a user over the Powershell the problem isn't there!

I testet the other Versions. I found out that all of the versions after 6.1.2 have this Issue. I Added the logs.

Thank you for your help

Thanks. So can you please verify that the 6.2.3 works and 6.2.4 does not?
(it might be easier to just try to login with the GUI)

Hi Martin,

I Tested all released versions from 6.1.2 to 6.5.3 and added the logs. The issue occured from 6.3.0 in every release.

I don't want to guide you in a wrong direction but maybe it has something to do with the "WebDAV/HTTP core upgraded to neon 0.33.0" Upgrade in 6.2.4 RC

Thanks in advance

Thanks. Though I was not able to identify anything useful.
Can you try to find out in what version of WinSCP was the problem introduced (if it is at all related to WinSCP version)?
You can find old versions of WinSCP at:
https://sourceforge.net/projects/winscp/files/WinSCP/

Hi Martin,

I added the Logs in a .zip. I hope you can access them (private file).
Just for your information I replaced some things because of security reasons.

Thank you for looking at that problem :)

Please post a session log file both from the old and the new version from the same enviornment.

Hello Together,

We have a C# project where we use the NuGet package of WinSCP and try to manage patches for a different software and download them from a Nextcloud via WebDAV.
Now switched from the version 6.1.2.0 to 6.5.3.0 (16364). The project is running in the background as a Windows Service as user System.

Now the problem:
with the new version we have problems to connect to the Nextcloud.
In the logs we see a lot of the following messages until the Proxy Server that we use for that closes the connection after 1 Minute.

Now that where it is getting weird.
When we execute the same code on the same machine as a User and not as System the connection can be build up (like we want to). We still see the messages for a few times but it generally works.
When we execute the same code on a different machine with the same proxy and in the same network and with the same operating system Windows Server 2019 (Build 17763) the code works in background as System and in foreground as a User.
Maybe I overlook something but I can't explain why that happens. In the old version we never had that issue.

I hope you can help me identify the issue if you need more information please tell me what you need.