PowerShell

PowerShell – The underlying connection was closed: An unexpected error occurred on a send.

What should have been just another quick PowerShell script performing a WebRequest to get some data, turned into a debugging session when both the Invoke-RestMethod and Invoke-WebRequest PowerShell commands were returning; The underlying connection was closed: An unexpected error occurred on a send.

Invoke-RestMethod

Here is the PowerShell Invoke-RestMethod response that returns: The underlying connection was closed: An unexpected error occurred on a send.

Invoke-RestMethod : The underlying connection was closed: An unexpected error occurred on a send.
At line:1 char:15
+ ... postdata2 = Invoke-RestMethod -Uri $post.URL -Method Get -UserAgent $ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-RestMethod], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeRestMethodCommand

Invoke-WebRequest

Here is the PowerShell Invoke-WebRequest response that returns: The underlying connection was closed: An unexpected error occurred on a send.

Invoke-WebRequest : The underlying connection was closed: An unexpected error occurred on a send.
At line:3 char:21
+ ... $postdata = Invoke-WebRequest -Uri $post.URL -Method Get -UserAgent $ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-WebRequest], WebException
+ FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand

Due to PowerShell defaults, it’s not unusual to have issues with TLS. The ambiguous nature of this error did however make me jump to the conclusion that I probably just needed to enforce TLS 1.2. This can be done using this PowerShell one-liner:

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12

However, in this situation that wasn’t the fix. Thinking it was still TLS related I checked out the SSL Certificate for the URI I was making my webrequests against. Looking at the certificate showed it was valid.

Solution

After a lot of searching I was able to work around the problem using scenarios from (here and here), however they weren’t ideal.

The resolution and solution I’m using to resolve the problem is to allow TLS, TLS 1.1 and TLS 1.2.

Insert the following line before invoking your PowerShell WebRequest using either Invoke-RestMethod or Invoke-WebRequest.

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls -bor [Net.SecurityProtocolType]::Tls11 -bor [Net.SecurityProtocolType]::Tls12

Summary

Hopefully this helps others experiencing this error, and allows me to quickly find it again next time I encounter this issue.

Also checkout my PowerShell Snippets Vol 1 and Vol 2 for other simple resolutions to ambiguous errors and tasks.

The underlying connection was closed: an unexpected error occurred on a send.

To resolve the PowerShell “underlying connection was closed” error, in your PowerShell script enable TLS:

Add the following line before your Invoke-RestMethod or Invoke-WebRequest call;

[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls -bor
[Net.SecurityProtocolType]::Tls11 -bor [Net.SecurityProtocolType]::Tls12

Applies To : PowerShell

Darren Robinson

Bespoke learnings from a Microsoft Identity and Access Management Architect using lots of Microsoft Identity Manager, Azure Active Directory, PowerShell, SailPoint IdentityNow and Lithnet products and services.