WebShield TCP half-close issue?

Avast Free Antivirus / Premium Security
1

I’m using Avast Free Antivirus 11.1.2253 with Virus definitions 160203-1.

I’m experiencing problems with AJAX requests sent from a client machine running Internet Explorer and the Avast client detailed above. It’s connecting to a web server on the same LAN, and everything works correctly if I disable Avast, but breaks if Avast is enabled.

I’m using Wireshark to compare network traces and can see a difference in behaviour when Avast is running. In both cases the short AJAX POST request is sent and the client half-closes the sending side of the connection ([FIN, ACK]) to wait for a response. In the broken case the client is then immediately sending a [RST, ACK] to terminate the connection. The reset seems to be something Avast is doing when it is enabled, and it’s issued before the server side has finished with its side of the connection.

Is this expected behaviour? Or a known issue?

Thanks!

2

Welcome to the forum. I’ve reported this to Avast.
That should get you an answer hopefully soon. :slight_smile:

3

Thanks for reporting, we’ll look into this.