On 13 Feb 2020, at 10:51, Fred Posner <fred(a)palner.com> wrote: Mark, There’s a module in Kamailio for uuid which would be generated by kamailio and may be useful in your needs. You may need the additional step of correlating the uuid to the call-I’d, but should be better prevention of injection type issues. -- Fred direct/sms +1 (336) 439-3733 > On Feb 13, 2020, at 4:57 AM, Daniel-Constantin Mierla <miconda(a)gmail.com> wrote: > > Hello, > > there are many things that can go wrong if a bad actor can forge sip > messages. That's why the call has to be authenticated/authorized in the > first place (either user/password or some other trusted relationship by > IP, certificate, ...). > > Now if a trusted actor tries to do bad things, then it is harder to > prevent, but once discovered, the identity is known and it can be > eventually published in a way or another (by laws and the commercial > agreement). > > Normally, the call-id should be randomly generated, with very low > chances of overlapping during the same time frame of active call. If > rtpengine is adding its own random part to file names, then the risk of > overwriting later is also very low. > > The dialog is identified by call-id, from tag (set by caller) and to tag > (set by callee), so in this case both caller and callee have to be bad > actors. > > But in many cases call-id is used alone as a key. Adding the from tag is > quite useless, because is set by the same UA, so if it wants to send > same call-id, can do the same with from tag. Then the to-tag is set by > the called side and during the call initiations, there can be many > outgoing branches, so during the 1xx phase there can be a couple of > to-tags flowing around. So if something needs to be stored in the early > phase, the to-tag of the to-be-answered call is not yet know. > > Rejecting new calls having the same callid as another recent one could > be safety check to plug if you are really concerned and you don't trust > completely who is making the call. You can easily use a htable for that, > to cache used call-ids and block new calls with same value. > > Cheers, > Daniel > >> On 13.02.20 10:07, Mark Boyce wrote: >> Hi all >> >> Over coffee we’ve been discussing the uniqueness and safety of call-id this morning. Lots of things like RTPEngine recording use call-id to generate filenames (yes it does escape them first :-). Not to mention dialog tracking (also uses from/to tags) etc. >> >> Which got us thinking. As call-id is determined by the first SIP packet that normally comes from a UA, should we care if this UA was broken or worse malicious? >> >> What would happen if they were repeated? For example we may struggle to determine a recordings owner in RTPEngine (file name format is callid+random.wav). >> >> For security should we be rejecting requests where we’ve seen the call-id before? >> >> >> All theoretical over coffee, as it was that or start working! >> >> Just wondering what peoples thoughts were? >> >> Cheers >> Mark >> _______________________________________________

On Thu, Feb 13, 2020 at 10:59:47AM +0000, Mark Boyce wrote: The trouble with that is it requires you to do a lot of gymnastics to keep extra state. Using Call-ID as a key allows you to operate on calls in a way that makes use solely of information contained in the SIP message itself. In an essentially thermodynamic sense, more state means more complexity, and more fragility due to the inevitable bugs and corner cases that any moving part and synchronisation effort brings. Call-IDs are required to be adequate GUIDs by the standard, and are sufficiently unique that the chance of a malicious collision is infinitesimal. Even short, bad GUIDs tend to be quite mathematically unique, unless they're just so comically short as to make a mockery of the GUID requirement. I would carefully weigh the economic and technical trade-offs of assigning calls UUIDs on your side and maintaining that mapping. A more pragmatic policy might be to reject requests with a Call-ID that is below a certain string length. -- Alex -- Alex Balashov | Principal | Evariste Systems LLC Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/ _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users

Hi Alex The thought process our side was more in these stages; - What if they’re not unique? - What would it affect? - Could it be used as an exploit? - If not do we care? … and wondered what others thought about it. I think you’re/Fred/Daniels points of a simple sanity check on them is probably the simplest/best answer. We can then reject a UA as too broken for us to want to deal with if it fails. We’ve also added a $dlg_var(dlg_uuid)=$uuid(g) just to tie some other state stuff in to Mark _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users