Re: [SR-Users] Kamailio vulnerable to header smuggling possible due to bypass of remove_hf

Thanks Daniel for patching up the bug, however I think you are downplaying severity of the problem at hand. You see, from the point of view of outside world, kamailio is not just engine and default config. All APIs that are provided are also part of the product, especially those "core" ones. As such, security issue with any such API is affecting the whole product. People using Kamailio expect those APIs do what documentation says they do, no more no less! What you are saying is basically any Kamailio installation any version under the sun except maybe dozen using default config is affected and has to be updated. My question therefore is "what Kamailio is going to do about it"? At the very least I'd expect fix to be merged into all actively maintained branches and official security advisory issued and distributed to all possible channels listing revisions and recommending upgrading ASAP. -Max On Tue., Sep. 1, 2020, 8:46 a.m. Daniel-Constantin Mierla, &lt;miconda(a)gmail.com <mailto:miconda@gmail.com>> wrote: Hello, thanks Sandro for directing a lot of time and effort for stress testing and fuzzing Kamailio, it really helps to increase the security and stability of the application. In a very short summary version, the issue was caused by a bug in extracting the name of non-common standard headers (like X-My-Hdr), not stripping the white spaces between the name and the following : (colon). The common standard headers (like From, To, Authorization, P-Asserted-Identity, ...) use a different header name parsing and there is no impact in them. The only security risk in my opinion is when some bad actor learns about the custom header names (and their body format/content) you use to pass data between Kamailio and other SIP systems in your core platform, then trying to preset such headers in the SIP traffic. Of course, security is affected only if you pass security sensitive data in such custom headers. The default kamailio.cfg is not using any custom headers, thus no impact on it. The config fix for it (without any code upgrade) is replacing: remove_hf("X-My-Hdr"); with: remove_hf_re("X-My-Hdr"); As a funny fact, I tracked the faulty code back to at least release SER v0.8.11, out 18 years ago, so it is a very long living bug. Cheers, Daniel On 01.09.20 14:44, Sandro Gauci wrote: affected has not upgraded or mitigated the header smuggling issue. of remove_hf <https://github.com/EnableSecurity/advisories/tree/master/ES2020-01-kamailio-remove-hf> 2020-07-16 to 2020-07-23 SIP headers from untrusted traffic to protect against header injection attacks by making use of the `remove_hf` function from the Kamailio `textops` module. These SIP headers were typically set through Kamailio which are then used downstream, e.g. by a media service based on Asterisk, to affect internal business logic decisions. During our tests and research, we noticed that the removal of these headers can be bypassed by injecting whitespace characters at the end of the header name. defined in `src/core/parser/hf.h`. found at the Communication Breakdown blog: https://www.rtcsec.com/2020/09/01-smuggling-sip-headers-ftw/. headers are used and processed by the affected logic. In a worst case scenarios, this vulnerability could allow toll fraud, caller-ID spoofing and authentication bypass. vulnerable setup which can be found at <https://github.com/EnableSecurity/advisories/tree/master/ES2020-01-kamailio-remove-hf/repro>. The following python code could then be used to reproduce the issue: 127.0.0.1:48017;rport;branch=z9hG4bK-%s\r\n" <http://sip:1000@127.0.0.1:48017>;transport=udp>\r\n" respond with a 200 OK while in a fixed version, Asterisk would respond with a 603 Decline response. This is specific to the [dialplan](https://github.com/EnableSecurity/advisories/blob/master/ES2020-0… in our example, which jumps to an internal dialplan if the `X-bypass-me` header is found. sufficiently address this security flaw. We recommend making use of the latest release or backporting the fixes where possible. Making use of regular expressions to cover white-space characters with `remove_hf_re` has been suggested as mitigation for this issue for cases where the code cannot be upgraded. the Kamailio Project for the very quick response and fix within minutes of our report being made available to him, as well as Torrey Searle for reporting this issue quickly to the Kamailio team. offensive security tools and provides quality penetration testing to help protect your real-time communications systems against attack. the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition. There are no warranties with regard to this information. Neither the author nor the publisher accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information. disclosure policy which can be found at <https://github.com/EnableSecurity/Vulnerability-Disclosure-Policy>. -- Daniel-Constantin Mierla -- www.asipto.com <http://www.asipto.com> www.twitter.com/miconda <http://www.twitter.com/miconda> -- www.linkedin.com/in/miconda <http://www.linkedin.com/in/miconda> Funding: https://www.paypal.me/dcmierla _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org <mailto:sr-users@lists.kamailio.org> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users