New Update Microsoft issues out-of-band update (KB5020435) to Windows 10 to fix connection issues


Level 85
Thread author
Honorary Member
Top Poster
Content Creator
Malware Hunter
Aug 17, 2014
Microsoft has released a new update (KB5020435) to Windows 10 machines to address an issue with Secure Sockets Layer (SSL) and Transport Layer Security (TLS) connections.

The highlights in this update are the same for Windows 10 20H2, 21H1, and 21H2, they read as follows:
  • We address an issue that might affect some types of Secure Sockets Layer (SSL) and Transport Layer Security (TLS) connections. These connections might have handshake failures. For developers, the affected connections are likely to receive one or more records followed by a partial record with a size of less than 5 bytes within a single input buffer. If the connection fails, your app will receive the error, “SEC_E_ILLEGAL_MESSAGE”.


Level 19
Top Poster
Jan 21, 2018
I had Win 10 connection problems over the weekend, installing this update sorted them. What was weird was that the router indicated that it was connected OK and monitoring the connection from PCs showed there was a connection. I could not access websites through Librewolf, Firefox or use Thunderbird, nor could I connect through Proton, Surfshark or Windscribe VPNs but I could use Tor and AdGuard VPN, I don't like the latter very much and it uses their own protocol. Installing this MS update means I can use all of these OK. Something to do with SSL and or TLS.


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