[Kamailio-Users] nonce_reuse protection issues

[Klaus Darilion]

Iñaki Baz Castillo schrieb:
> 2009/7/16 Klaus Darilion <klaus.mailinglists at pernau.at>:
>> Hi!
>>
>> I really wonder if the nonce_reuse protection feature is useful and if
>> anybody uses it without problems.
>>
>> One problem I have is with retransmission: e.g:
>>
>> ----INV1 --->
>> <---407------
>> ----ACK----->
>>
>> ----INV2------>
>>   here happens a delay to the INVITE (e.g. jam in the access uplink,
>> SIP proxy slow, ... whatever) which causes a retransmission of the INVITE
>>
>> ----INV3------> (retransmission of INV2)
>>
>> the proxy processes INV2, authenticates the user successful and forwards
>> the requests
>>
>> then the proxy processes INV3, finds out that the nonce is reused and
>> sends back 407 --> client gives up, but the request was also forwarded
>> by the proxy :-(
> 
> Yes, that occurs if no transaction was already created.
> 
> 
> 
>> How do you handle such a scenario? Do you always create the transaction
>> before authentication?
> 
> Creating the transaction before authentication could be dangerous (DOS
> attacks). I suggest to create the transaction manually *just* after
> authentication (before t_relay and previous routing logic accessing to
> DB and so).

Yes. Because that would require to handle also registrations 
transaction-stateful.

>> One other thing I just found out is that reuse-check is done after
>> successful authentication - shouldn't it be done the other way round?
> 
> True. However, to anounce "stale=true" in 401/407 response the
> credentials must be verified.

It would be sufficient to check if the nonce is reused, response 
calculation could be done afterwards

> Imagine that a phone sends a request with an already used nonce (very
> common behaviour) and the proxy replies 401/401 without "stale"
> parameter. Then the phone could understand that the user/password are
> wrong and wouldn't try to authenticate again.
> "stale" parameter in 401/407 means that the credentials are valid
> (user, password and nonce are valid) but the nonce already expired in
> the server so the client must create a new credentials with the new
> nonce received in the 401/407.

yes.

IMO disabling nonce-reuse does not get you much security benefits, just 
increased SIP traffic. Thus nonce-reuse should be enabled by default.

regards
klaus