[Kamailio-Users] nonce_reuse protection issues

[Daniel-Constantin Mierla]

On 16.07.2009 17:32 Uhr, Klaus Darilion wrote:
>
>
> 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.
in 1.5, registrar module sends reply in stateful mode if transaction was 
created for REGISTER -- it uses send_reply() from sl which binds to tm 
if available.


>
>>> 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.

I have disabled it is most of the configs I have. If there are 
retransmission, things may get nuts.

In SR, modules_s/auth has it disabled by default. We should move and 
discuss on devel to see the impact/benefits and decide the default value.

Cheers,
Daniel

-- 
Daniel-Constantin Mierla
http://www.asipto.com/index.php/sip-router-bootcamp/