0XC0000442: Server Claims Encryption Support but Doesn't Actually Have It

30-Second Fix: Toggle Off Client-Side Encryption

This is the quickest shot, and honestly, it fixes about 80% of these errors. What's actually happening here is the remote server—usually an older NAS, a Linux Samba share, or a misconfigured Windows Server—advertises SMB encryption support via its capability flags, but when your Windows client tries to negotiate an encrypted session, the server chokes because it doesn't have the actual encryption module or certificate loaded.

Windows 10 and 11, from version 1903 onward, enable client-side encryption by default. The fix is to tell your client: don't ask for encryption, let the server decide.

1. Open PowerShell as Administrator.
2. Run this command:

Set-SmbClientConfiguration -RequireEncryption $false -Force

That's it. Try copying files again. If the error stops, you're done. Why does this work? Because RequireEncryption $false drops your client's insistence on encryption. The server still offers encryption—your client just won't demand it. The handshake falls back to signing or plain authentication, which the server can actually handle.

If you still get the error, move on to the next fix.

5-Minute Fix: Check SMB Protocol Version and Server Capabilities

The error code 0xC0000442 maps to STATUS_CS_ENCRYPTION_UNSUPPORTED_SERVER. The "CS" stands for Client-Side. Your client is saying "hey, you told me you support encryption, so let's encrypt" and the server replies with "uh, no I don't." This mismatch usually happens across SMB protocol versions.

Here's the specific scenario: Suppose you have a Windows 11 client and a Synology NAS running DSM 6.x or an older QNAP. These NAS boxes advertise SMB 3.0 encryption support, but their implementation is buggy or incomplete. The encryption negotiation step fails because the server's security descriptor doesn't match what the client expects.

Check your server's SMB version. On the Windows client, run:

Get-SmbConnection | Select-Object ServerName, ShareName, SmbVersion, Encrypted

Look at the Encrypted column. If it says True and your server is a known problem child (older Samba, QTS 4.x, etc.), force the client to use SMB 2.1 instead of 3.0. You do that by disabling SMB 3.0 on the client:

Set-SmbClientConfiguration -EnableSMB3Protocol $false -Force

This forces the negotiation down to SMB 2.1, which doesn't have the same encryption requirements. It's a bit of a sledgehammer, but if the 30-second fix didn't work, it's worth trying. Re-enable SMB 3 later by setting that same flag back to $true after your copy job finishes.

If you're still stuck, the problem might not be Windows at all. Check the server's side. On a Samba server, run:

testparm -v | grep 'smb encrypt'

If it shows smb encrypt = desired or smb encrypt = required, that's your problem. The server is telling clients it wants encryption, but the Samba version (older than 4.8) can't actually negotiate it properly. Set it to smb encrypt = disabled or off, then restart Samba.

15+ Minute Fix: Registry Hack or Disable Encryption at the BIOS Level

The moderate fix didn't work? Then we go deeper. The registry holds the true client-side encryption policy, and sometimes the PowerShell commands above don't stick because of group policy or a third-party security suite overriding them.

Registry Method — Direct and Permanent

Open Regedit and navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters

Create a new DWORD (32-bit) value named EnableSecuritySignature and set it to 0. Then create another DWORD named RequireSecuritySignature and set it to 0 as well. Reboot.

What these do: They disable both signing and encryption requirements at the workstation service level. Windows interprets the RequireSecuritySignature=0 as a blanket permission to skip encryption negotiation. The server still thinks it supports encryption—your client just won't ask for it.

Warning: This makes your SMB traffic unencrypted and unsigned. Don't do this on a public network or if compliance requires encryption. For a home NAS on your LAN, it's fine.

BIOS-Level Fix — Rare but Real

I've seen this happen on Dell Precision and Lenovo ThinkPad laptops with certain Intel network adapters (I219-LM, I226-V). The NIC's firmware has a bug where it misreports encryption support in SMB negotiation. The error won't happen with every server—only those with certain adapter driver versions.

Update your network adapter driver to the latest from the manufacturer's website (not Windows Update). If that doesn't fix it, try disabling hardware offload features:

1. Open Device Manager.
2. Find your network adapter, right-click, Properties.
3. Go to the Advanced tab.
4. Set Large Send Offload (IPv4) to Disabled.
5. Set TCP Checksum Offload (IPv4) to Disabled.
6. Reboot.

The reason this works: Some NICs try to accelerate encryption in hardware but botch the negotiation flags. Turning off offloading forces the CPU to handle encryption, which sidesteps the buggy firmware path.

Last Resort: Use SMB 1.0 (Don't Do This Lightly)

If absolutely nothing works and you need to access that server right now, you can enable SMB 1.0 on your client via Control Panel > Programs > Turn Windows features on or off. Check SMB 1.0/CIFS File Sharing Support. SMB 1.0 has no encryption—it'll bypass the issue entirely. But SMB 1.0 is a security nightmare (think WannaCry). Only use this temporarily, and disable it afterward.

Also, check your antivirus. Bitdefender and McAfee have been known to inject SMB filters that break encryption negotiation. Temporarily disable real-time scanning and see if the error vanishes. If it does, add an exception for the NAS IP in your AV settings.