Modern Windows cannot access myServer SMB shares because guest access is enabled

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2 weeks 5 days ago - 2 weeks 5 days ago #5121 by CrabbyPatties
I have faced difficulties accessing myServer’s Samba shares from Windows since receiving my Allonis remote. Some PCs would access the shares, while others gave the rather unhelpful error:

“Windows cannot access \\[server]\myServer … your organisation’s security policies block unauthenticated guest access” (error 0x800704f8).

I believe I have finally got to the bottom of the underlying issue.

The supplied Samba configuration on my system had:

map to guest = Bad User

and both the myServer and myMedia shares had:

Public = yes
Guest ok = yes

This means that a new Windows computer tries to connect as a guest rather than being asked for credentials. Modern Windows blocks insecure guest SMB access by default, so it fails before presenting a login prompt. A PC which has already established an authenticated connection can appear to work, which makes the issue particularly confusing.

Changing the configuration so that guest access is not offered, and requiring the existing allonis Samba user for the shares, resolved it immediately:

[global]
map to guest = Never
usershare allow guests = no

[myServer]
guest ok = no
valid users = allonis

[myMedia]
guest ok = no
valid users = allonis

A new Windows PC now gets the expected credentials prompt once, can save the allonis credentials, and then accesses the shares normally thereafter.

Note... this also affected myDesigner 6, which depends on the SMB \\server\myServer file share to access wwwroot, as well as the myServer backend. It worked again once Windows had an authenticated connection to the same SMB target specified in myDesigner’s File Share setting. In my case I used \\192.168.0.162\myServer; using the server name should also work, provided the Windows credential is saved for that hostname.

Would it be possible for Allonis either to use authenticated SMB shares as the default configuration, or to document this clearly in the Windows setup guidance? It would have saved me a great deal of head-scratching.
Last edit: 2 weeks 5 days ago by CrabbyPatties.
The following user(s) said Thank You: andrew

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2 days 17 hours ago #5124 by davep
Thanks for posting this. An old dog learned something today. Today's server update will automatically patch the existing samba configuration file when it starts up. Testing shows that it works and there is no adverse side effects for people who have already authenticated with the server.

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