16 Jul
2009
16 Jul
'09
12:04 p.m.
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 :-(
How do you handle such a scenario? Do you always create the transaction
before authentication?
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?
regards
Klaus
16 Jul
16 Jul
2:50 p.m.
2009/7/16 Klaus Darilion <klaus.mailinglists(a)pernau.at>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).
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.
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.
--
Iñaki Baz Castillo
<ibc(a)aliax.net>
5:32 p.m.
Iñaki Baz Castillo schrieb:
It would be sufficient to check if the nonce is reused, response
calculation could be done afterwards
2009/7/16 Klaus Darilion
<klaus.mailinglists(a)pernau.at>at>:
Yes. Because that would require to handle also registrations
transaction-stateful.
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). 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. 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
6:11 p.m.
2009/7/16 Klaus Darilion <klaus.mailinglists(a)pernau.at>at>:
Iñaki Baz Castillo schrieb:
What I mean is that, response calculation should be done even if nonce
is reused. If not, there is no way to send "stolen=true" in 401/407.
--
Iñaki Baz Castillo
<ibc(a)aliax.net>
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
9:18 p.m.
Iñaki Baz Castillo wrote:
2009/7/16 Klaus Darilion
<klaus.mailinglists(a)pernau.at>at>:
I do not understand this. If the nonce was already use, the proxy could
respond immediately with 407 and "stale=true" without checking the password
regards
klaus
Iñaki Baz Castillo schrieb:
What I mean is that, response calculation should be done even if nonce
is reused. If not, there is no way to send "stolen=true" in 401/407. 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
10:16 p.m.
El Jueves, 16 de Julio de 2009, Klaus Darilion escribió:
Iñaki Baz Castillo wrote:
Hummm, yes it could... good point :)
--
Iñaki Baz Castillo <ibc(a)aliax.net>
2009/7/16 Klaus Darilion
<klaus.mailinglists(a)pernau.at>at>:
I do not understand this. If the nonce was already use, the proxy could
respond immediately with 407 and "stale=true" without checking the password
Iñaki Baz Castillo schrieb:
What I mean is that, response calculation should be done even if nonce
is reused. If not, there is no way to send "stolen=true" in 401/407. 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 
21 Jul
21 Jul
12:38 p.m.
On 16.07.2009 17:32 Uhr, Klaus Darilion wrote:
It would be sufficient to check if the nonce is reused, response
calculation could be done afterwards
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/
Iñaki Baz Castillo schrieb:
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.
2009/7/16 Klaus Darilion
<klaus.mailinglists(a)pernau.at>at>:
Yes. Because that would require to handle also registrations
transaction-stateful. 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). 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. 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.
5613
days inactive
5618
days old
6 comments
3 participants
participants (3)
-
Daniel-Constantin Mierla -
Iñaki Baz Castillo -
Klaus Darilion