Disabling SMB1 by default

David Mulder dmulder at suse.com
Tue Jun 20 12:18:03 UTC 2017

The negotiate always begins with an SMB1 negotiate, and indicates
whether SMB2+ is supported (this is called a multi-protocol negotiate).
So, it doesn't work that way. If you disable SMB1, then it starts with
SMB2+ negotiate. It doesn't 'fallback' to previous versions, it starts
at the lowest supported and moves up. That's how the protocol is defined.
So, enabling SMB3 by default will allow clients to negotiate up to SMB3
if supported, but will also continue to support older versions.

On 06/20/2017 06:01 AM, Andreas Hasenack via samba-technical wrote:
> On Mon, Jun 19, 2017 at 8:14 PM, Jeremy Allison <jra at samba.org> wrote:
>> On Tue, Jun 20, 2017 at 10:20:07AM +1200, Andrew Bartlett via
>> samba-technical wrote:
>>> On Mon, 2017-06-19 at 15:39 +0200, Stefan Metzmacher via samba-
>>> technical wrote:
>>>> Hi Andreas,
>>>>> we recently had a bug filed against Ubuntu [1] requesting that we
>> disable
>>>>> the SMB1 protocol by default. That is part of a larger campaign [2]
>> to get
>>>>> rid of SMB1 entirely.
>>>>> Has there been any discussion among Samba developers to change the
>> default
>>>>> client and server min protocol level to SMB2? Would you consider
>> making
>>>>> such a change?
>>>> We're recently discussed changing 'client max protocol = SMB3' so
>>>> that smbclient and other utilities work against servers
>>>> with disabled SMB1 by default.
>>>> We hope to get this into 4.7, but there's only about 3 weeks
>>>> left to make this change (until 4.7.0rc1 is branched from master),
>>>> so it's not sure if such a change will make it into 4.7.0 (released
>>>> in September).
>>> I had the dates as giving us 2 weeks.  Yes, there isn't much time.
>> Yeah, that's too short a time to do anything really. IMHO we
>> just need to help people on the list to turn what they can
>> off themselves for now, and work on how to do the migration
>> properly over the next year or so.
> What is the big issue with allowing the client to try SMB3 first? Won't it
> fallback to SMB2, then NT1, and so on?
> Won't many server admins have disabled SMB1 in their windows servers after
> the wannacry attack?

David Mulder
SUSE Labs Software Engineer - Samba
dmulder at suse.com
SUSE Linux GmbH, GF: Felix Imend├Ârffer, Jane Smithard, Graham Norton, HRB 21284 (AG N├╝rnberg)

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