WebClient SSL Error: "System.Net.WebException: The SLL connection could not be established"

Question

Hi, dear stranger!

I made a console application for my telegram bot. On my laptop it works perfectly, but on my PC which i want to use as a server this code gets an error. I spent the whole day trying to fix it and went through a lot of similar topics over here but didn't find any solution.

The trouble appears at this part of code:

try {
    var webClient = new WebClient();
    webClient.DownloadString($"{startUrl}/sendMessage?chat_id={messageFromId}&text=" + number.ToString());
}

 catch (Exception e){
    Console.WriteLine(e.ToString());
}

How can i avoid SSL certificate since i am not looking for a real security here?

The error is below:

> System.Net.WebException: The SSL connection could not be established,
> see inner exception. Unable to read data from the transport
> connection: Удаленный хост принудительно разорвал существующее
> подключение..  ---> System.Net.Http.HttpRequestException: The SSL
> connection could not be established, see inner exception.  --->
> System.IO.IOException: Unable to read data from the transport
> connection: Удаленный хост принудительно разорвал существующее
> подключение..  ---> System.Net.Sockets.SocketException (10054):
> Удаленный хост принудительно разорвал существующее подключение.    ---
> End of inner exception stack trace ---    at
> System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.ThrowException(SocketError
> error, CancellationToken cancellationToken)    at
> System.Net.Sockets.Socket.AwaitableSocketAsyncEventArgs.GetResult(Int16
> token)    at System.Net.FixedSizeReader.ReadPacketAsync(Stream
> transport, AsyncProtocolRequest request)    at
> System.Net.Security.SslStream.ThrowIfExceptional()    at
> System.Net.Security.SslStream.InternalEndProcessAuthentication(LazyAsyncResult
> lazyResult)    at
> System.Net.Security.SslStream.EndProcessAuthentication(IAsyncResult
> result)    at
> System.Net.Security.SslStream.EndAuthenticateAsClient(IAsyncResult
> asyncResult)    at
> System.Net.Security.SslStream.<>c.<AuthenticateAsClientAsync>b__65_1(IAsyncResult
> iar)    at
> System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult
> iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean
> requiresSynchronization)
> --- End of stack trace from previous location where exception was thrown ---

What i've already tried:

1) Puting this before the WebClient request. Doesn't help:

ServicePointManager.ServerCertificateValidationCallback +=
   delegate (object sender, X509Certificate certificate, X509Chain chain,
          SslPolicyErrors sslPolicyErrors)
   {
       return true;
   };

2) Using delegates to disable SSL

ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };

3) Your idea is next?

Or may be i just was using wrongly the previous solutions? Don't pass by, let's try your ideas!

Thanks!

https://learn.microsoft.com/en-us/dotnet/framework/network-programming/tls?view=netframework-4.7.2 — Lex Li, May 23 '20 at 02:03
Thanks! I'm checking this MSDN page right now. Can you be more precise since it seems that you know the answer? I tried this trick and it didn't work ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; — Funny Fat Man, May 23 '20 at 10:24
Also i can't get how and why it works on my laptop with Win 10 and doesn't on another machine with Win 8 — Funny Fat Man, May 23 '20 at 10:28
I believe that article talks about much more than just ignoring certificate check. Be patient and read everything through. — Lex Li, May 23 '20 at 13:30

score 0 · Answer 1 · answered Jul 06 '20 at 13:15

Sometimes the cause of such error is old version of TLS protocol, for instance when client application uses TLSv1.0 - which usually is deprecated (not permitted) on the server side. In this case SSL server usually simply drops the connection and therefore, the client throws this exception.
So it makes sense to try enabling TLS1.1 & TLS1.2 for you client(depends on the framework version you use). Just google the corresponding error description on English (which seems to be - "An existing connection was forcibly closed by the remote host")

Thank you for the reply! Fortunately i've found a reason why it didn't work. I was working with Telegram which was blocked at the moment in Russia.So my requests weren't working at all. I fixed this by using proxies ;) — Funny Fat Man, Jul 07 '20 at 16:38

score 0 · Answer 2 · answered Jul 07 '20 at 16:40

0

Fortunately i've found a reason why it didn't work. I was working with Telegram which was blocked at the moment in Russia.So my requests weren't working at all. I fixed this by using proxies. Case solved.

answered Jul 07 '20 at 16:40

Funny Fat Man

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WebClient SSL Error: "System.Net.WebException: The SLL connection could not be established"

2 Answers2