Windows Update must not obtain updates from other PCs on the Internet.

From Windows 10 Security Technical Implementation Guide

Associated with: CCI-000366

SV-80171r2_rule Windows Update must not obtain updates from other PCs on the Internet.

Vulnerability discussion

Windows 10 allows Windows Update to obtain updates from additional sources instead of Microsoft. In addition to Microsoft, updates can be obtained from and sent to PCs on the local network as well as on the Internet. This is part of the Windows Update trusted process, however to minimize outside exposure, obtaining updates from or sending to systems on the Internet must be prevented.

Check content

If the following registry value does not exist or is not configured as specified, this is a finding: Registry Hive: HKEY_LOCAL_MACHINE Registry Path: \SOFTWARE\Policies\Microsoft\Windows\DeliveryOptimization\ Value Name: DODownloadMode Value Type: REG_DWORD Value: 0x00000000 (0) - No peering (HTTP Only) 0x00000001 (1) - Peers on same NAT only (LAN) 0x00000002 (2) - Local Network / Private group peering (Group) 0x00000063 (99) - Simple download mode, no peering (Simple) 0x00000064 (100) - Bypass mode, Delivery Optimization not used (Bypass) A value of 0x00000003 (3), Internet, is a finding. Prior to v1607 of Windows 10, acceptable options include: 0x00000002 (2) - Local network / Private group peering (Group) 0x00000001 (1) - Peers on the same NAT only (LAN) 0x00000000 (0) - None

Fix text

Configure the policy value for Computer Configuration >> Administrative Templates >> Windows Components >> Delivery Optimization >> "Download Mode" to "Enabled" with any option except "Internet" selected. Acceptable selections include: Bypass Group HTTP only LAN Simple Prior to v1607 of Windows 10, acceptable selections include: Group LAN None

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