Block Insecure Protocols
This registry value controls which network protocols supported Microsoft 365 apps for Windows can use when opening documents.
since 0.9.8.11
Purpose
Show registry keys (1)
HKCU\software\policies\microsoft\office\16.0\common\fileio\blockinsecureprotocols
This registry value controls which network protocols supported Microsoft 365 apps for Windows can use when opening documents. Its data type is REG_DWORD.
A value of 1 blocks documents from being opened through non-HTTPS connections, including unencrypted HTTP and FTP locations. A value of 0 allows all protocols and corresponding links.
Notes
Additional effects
When blocking is enforced, users cannot override the restriction in Trust Center. Because the value is stored under HKCU, it applies to the Windows user associated with that registry hive.
Security
HTTP and FTP do not provide the transport encryption available with HTTPS. Data or credentials exchanged while accessing a document can therefore be intercepted or modified by an attacker who controls part of the network path. Preventing Office from opening documents through these protocols reduces exposure to eavesdropping and adversary-in-the-middle attacks.
This setting does not establish that a document delivered over HTTPS is trustworthy or free of malicious content. Other Office security controls continue to apply.
Possible side effects
Documents hosted by servers or applications that offer file access only through HTTP, FTP, or another non-HTTPS protocol can no longer be opened through that path in affected Office applications. This can disrupt older document-management systems, intranet resources, and links to legacy file repositories.
Notes
The office\16.0 registry path and the “Microsoft Office 2016” policy category are part of the shared namespace used by the Office administrative templates. Their names alone do not mean that every perpetual Office 2016 release supports this newer setting.
Microsoft documentation
Microsoft Learn: Block insecure protocols for file opens in Microsoft 365 apps
Microsoft Learn: Microsoft 365 Apps for Enterprise security baseline settings