[Kamailio-Users] uac_replace_from check

[Juha Heinanen]

Daniel-Constantin Mierla writes:

 > Indeed, there can be an extra check there. Not sure how much protection 
 > it adds here. When X calls Y, if caller is trusted (e.g., auth user, 
 > trusted peer) then either call goes to costly resource (PSTN) that is 
 > also trusted, to a local user or untrusted destination, case in which 
 > you route only if does not cost you anything. If local users are not 
 > trustable and use "custom UA", then replies can go to first Via, 
 > skipping the rest of Via stack, ignoring negative replies after 200ok. 
 > Unless there is symmetric nat and they are forced to use the proxy, the 
 > safest will be a b2bua.

i don't understand, how the above relates to the security issue that i
brought up.  it has nothing to do with cost, but a possibility to make
uac send in-dialog requests so that they by-pass the proxy.  nasty
things documented earlier can happen if that is not prevented.

 > Say you get a 200OK to an INVITE with spoofed r-r, should it be
 > dropped?

definitely yes.  there could, for example, be a flag that tells if the
check needs to be done, so that you don't waste resources needlessly if
uas is trusted.

-- juha