Avast antivirus probably blocking all my web browsers connection

Avast Free Antivirus / Premium Security
1

Afer update avast antivirus premium security to the newest version , I started to notice that randomly my web browsers (chrome, firefox and edge) are blocked and I cannot have access to web pages. Only solution for me is to restard windows or uninstall avast application. Turn off avast protection and firewall didin’t work.

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2

I had similar for last 10 days but only affected a handful of sites like some forums, facebook, youtube, speed test.

Have you got a vpn or added add blockers? turns out for me anyway add block ultimate extention add on was the culprit. turned off the blocker for each page and everything is working fine now.

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3

I don’t use VPN , have ublock origin on firefox , but internet problem is affected in all my browsers like chrome where i don’t have any extensions like add blocker , even typing in command promt “ ping google com” says that i have no connection to WAN ,strange

4

Soz but i have no idea then as i only use firefox.

hopefully someone else will be along to advise.

5

I’ve had the exact same problem for a few days on several computers. I had to disable the firewall or completely disable Avast to get it working again. I’m on Windows 10 Pro.

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6

Reposting my findings here (as I posted in the other thread #848193):

Hi there,

Running 25.9.10453g (version 25.9.10453.0) on Windows 10 Pro 22H2

I’ve been using Avast for 15+ years now and it’s my first time reporting an issue but it’s quite an annoying one.

It started approximately 3 days ago where my browsers (Firefox and Chrome) stopped loading any URL. I first thought it was some stupid DNS lookup issue or my ISP getting crazy but every other apps were fine (Slack, Discord) and my phone on the same network was ok.

Rebooted the computer, problem went away, I thought it was one of those one offs bug. But the next day it happened again so I digged further and found out that Avast stopped working somehow and the temporary fix was to disable then re enable all agents.

I have checked the EventViewer in Windows and found there was an application error associated to the time when the problem kicks off associated with the ucrtbase.dll file.

Here’s the full XML view of the Event if that helps:

- <Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
- <System>
  <Provider Name="Application Error" /> 
  <EventID Qualifiers="0">1000</EventID> 
  <Version>0</Version> 
  <Level>2</Level> 
  <Task>100</Task> 
  <Opcode>0</Opcode> 
  <Keywords>0x80000000000000</Keywords> 
  <TimeCreated SystemTime="2025-09-24T10:19:37.7833715Z" /> 
  <EventRecordID>121395</EventRecordID> 
  <Correlation /> 
  <Execution ProcessID="0" ThreadID="0" /> 
  <Channel>Application</Channel> 
  <Computer>Raphael-DESKTOP</Computer> 
  <Security /> 
  </System>
- <EventData>
  <Data>AvastSvc.exe</Data> 
  <Data>25.9.10453.0</Data> 
  <Data>68c00b4c</Data> 
  <Data>ucrtbase.dll</Data> 
  <Data>10.0.19041.3636</Data> 
  <Data>81cf5d89</Data> 
  <Data>c0000409</Data> 
  <Data>000000000007286e</Data> 
  <Data>1184</Data> 
  <Data>01dc2d281b5ec39f</Data> 
  <Data>C:\Program Files\Avast Software\Avast\AvastSvc.exe</Data> 
  <Data>C:\WINDOWS\SYSTEM32\ucrtbase.dll</Data> 
  <Data>923d679e-e774-4cb3-b83d-4554f00a445a</Data> 
  <Data /> 
  <Data /> 
  </EventData>
  </Event>