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Subject: Re: [mqtt] Connect with existing ID


This is essential for stuck clients, clients that don't realise they've got a dead connection and reconnect, clients taking over when a node's unresponsive, etc. The same functionality exists in AMQP, where it features at the link level - there it's called link stealing. Think of it as STONITH for mq clients.

It shouldn't be a security hole if you're authenticating and authorising your clients. It may not be clear that's needed - if you like, you might want to add a JIRA.

It's a pain in the neck to implement, too, as a server, as it's the only time one connection 'needs to know' about another.

Raphael Cohn
Chief Architect, stormmq
Co-Chair, OASIS MQTT Standard
Secretary, OASIS AMQP Standard
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On 15 November 2013 15:36, Paul Fremantle <paul@wso2.com> wrote:
I never before noticed this line in the input spec:

If a client with the same Client ID is already connected to the server, the "older" client must be disconnected by the server before completing the CONNECT flow of the new client.

It corresponds to this in the WD:

If the ClientId represents a client already connected to the server then the server MUST disconnect the existing client.

Isn't this a bit of a security hole? If I can guess a ClientID I can disconnect it. If there is anyone using the clientId as a topic for replies and relying on clientId for security (e.g. in Mosquitto's ACL %c to match the client id of the client), then this is also a security hole. 

Can anyone comment?


Paul Fremantle
CTO and Co-Founder, WSO2
OASIS WS-RX TC Co-chair, Apache Member

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blog: http://pzf.fremantle.org

wso2.com Lean Enterprise Middleware

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