Random Port Exhaustion on Sophos Endpoint Security and Control clients version 10.6.3 and 10.6.4 on Windows 10 Enterprise workstations.

I believe this is fixed in swi_fc.exe in a later version.  What is the version of swi_fc.exe that is running?  The file is typically here:
"C:\Program Files (x86)\Common Files\Sophos\Web Intelligence\swi_fc.exe".

I assume you're not Central but SEC managed?

If you first run (admin prompt):
tasklist | find "swi_fc.exe"

To find the pid of swi_fc.exe.  Example output:

swi_fc.exe 4196 Services 0 16,164 K

In this case 4196, then run:
netstat -anoq | find "BOUND" | find "4196" /c
This will count all the connections attributed to swi_fc.exe that are in the bound state.

When all the browser processes (chrome.exe, firefox.exe, iexplore.exe, etc..) are closed this should be 0 as swi_fc.exe shouldn't be proxying anything just listening.  

Is this what you see?  I assume when you have the issue, this count goes up into the thousands?

If so, this should be fixed in a future swi_fc.exe.  The bound ports accumulate for connections that are made by swi_fc.exe that get ACCESS_DENIED, ERROR_SEM_TIMEOUT for example.

For example, if I create a local Windows Firewall rule to block an outgoing TCP connection to a specific address and then visit this address, swi_fc.exe would get ACCESS_DENIED back from Get­Queued­Completion­Status API.  This would cause 1 BOUND socked. 

If I have an upstream device which is blocking an address and swi_fc.exe makes a connection it might get back ERROR_SEM_TIMEOUT.  For each of these, I suspect it's keeping the connection in the BOUND state.

Given this, do you have a device upstream blocking sites being accessed such that nothing is returned, i.e. not a block page?  More of a stealthy drop of the connection attempt?

If you try the Sophos Central client (can create a trial via cloud.sophos.com and deploy to a test client), you could copy the swi_fc.exe from that version to "C:\Program Files (x86)\Common Files\Sophos\Web Intelligence\swi_fc.exe". To replace it you would need to stop all the browser processes and then stop the Sophos Web Filter service before restarting the Sophos Web Filter service which will start the new swi_fc.exe process.

Hope it helps.

Regards,
Jak

Amazing, thank you Jak! I will check out what you have suggested next time it occurs to one of our users. Do you know what version of "swi_fc.exe" this should be fixed in for an on-prem solution, or should I raise a ticket with the support desk?

Although I cannot prove it, my suspicion is that this might be linked to a SCF issue we've started having on Win10 where localhost traffic is not being detected correctly as localhost and is then subsequently being blocked inbound by the SCF. 

Thanks again for your help!

Tom 

Amazing, thank you Jak! I will check out what you have suggested next time it occurs to one of our users. Do you know what version of "swi_fc.exe" this should be fixed in for an on-prem solution, or should I raise a ticket with the support desk?

Although I cannot prove it, my suspicion is that this might be linked to a SCF issue we've started having on Win10 where localhost traffic is not being detected correctly as localhost and is then subsequently being blocked inbound by the SCF. 

Thanks again for your help!

Tom