Note: The Internet Explorer 11 desktop application will be retired and go out of support on June 15, 2022 (for a list of what's in scope, see the FAQ). The same IE11 apps and sites you use today can open in Microsoft Edge with Internet Explorer mode. Learn more here.


When Internet Explorer 11 or Internet Explorer 10 establishes a new WebSocket connection to a WebSocket server over Secure Sockets Layer (SSL) through a proxy server, the number of active connections increases. After that connection is closed, the number of active connections does not decrease. Therefore, you can't establish a new connection to this WebSocket server after 12 connections because there is no available free connection.


To fix this problem, install the most recent cumulative security update for Internet Explorer through Microsoft Update. Additionally, see the technical information about the most recent cumulative security update for Internet Explorer.

Note This update was first included in the MS16-001: Security update for Internet Explorer: January 12, 2016.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.


Learn about the terminology that Microsoft uses to describe software updates.

For more information about the WebSocket feature, see the WebSocket API.

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