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

Alex Balashov abalashov at evaristesys.com
Wed Sep 2 19:56:54 CEST 2020

For whatever it's worth: IHO, the official project response to this 
issue, and Daniel's in particular, was reasonable and proportional to 
the severity of the problem.

As Daniel pointed out in his response:

1. "Of course, security is affected only if you pass security sensitive 
data in such custom headers"

2. "The default kamailio.cfg is not using any custom headers, thus
no impact on it."

Or in other words: This is not a ubiquitous problem affecting a large 
proportion of the installed base. Custom headers present a security risk 
_ipso facto_. It is up to the implementor to make a reasonable and 
informed risk assessment about using them.

It is true that #2 is less of a mitigating factor than #1; as someone 
pointed out, the value of Kamailio is tied up in the core APIs it 
provides as a "toolkit", rather than packaged configurations, as most 
substantial implementations of Kamailio involve advanced use-cases and 
extensive custom config-writing.

Nevertheless, some subsequent responses in this thread seem like 
needless hyperventilation to stimulate "political energy" or energise 
some kind of online outrage machine. This betrays a failure to see 
forest for trees and a lack of adequate perspective on the objective 
impact of this issue (medium), or a penchant for hysteria.

-- Alex

On 2020-09-02 13:48, jbrower at signalogic.com wrote:
> Maxim is correct. *Anything* even remotely exploitable must be 
> documented, fixed, and reported. Credibility with company security 
> officers, CFOs -- even with the press if something bad should ever 
> happen -- is crucial.
> Whether there is an impacted standard is irrelevant. What standard ever 
> covered RowHammer, Spectre, etc ?  If the exploit doesn't make sense 
> because "they would have access to other private data anyway" is an 
> assumption and therefore also irrelevant. Sophisticated hackers are 
> great programmers (as are Kamailio programmers), they work 24/7 (as we 
> do) -- who's to say how they might combine exploits in some way we 
> cannot yet imagine.
> -Jeff
> Quoting Maxim Sobolev <sobomax at sippysoft.com 
> <mailto:sobomax at sippysoft.com>>:
>> Hey Daniel, Henning, Tao,
>> Thanks for commenting out. There are a lot of opinions for me to 
>> address individually, so I will just clarify my opinion. The only 
>> substantial difference I think is whether the issue at hand warrants a 
>> security advisory to be issued by the Kamailio project or not. I 
>> totally think that it does, but it looks like I am in the minority here.
>> Why do I think this way? Well, the first argument is a bit empirical. 
>> It is hard to generalize out of sample size 1, but in like 90% 
>> engagements where I had to use SIP Proxy element and integrate it with 
>> different SIP elements I ended up using "private headers" for passing 
>> information between elements within that setup. So the task of 
>> cleaning up those headers at the edge of the network is very relevant 
>> at least to some users. It also matches Sandro's assessment, which 
>> gives it at least some credibility.
>> Second, a more general one. Not only I have some experience in 
>> software development field, but also I got a chance to participate in 
>> much bigger and older open source projects (i.e. FreeBSD Project, 400+ 
>> active developers, 1,000+ contributors) so I have seen how security is 
>> dealt with properly in a mature open source project. You guys might 
>> fancy the fact that Kamailio issued the last security advisory in 2018 
>> as a "code quality" indicator, but to me that shows a total lack of 
>> proper security process.  With the code base of its size, I'd expect 
>> at least several security issues of various criticality being found 
>> per year. I frankly don't understand the pushback I am getting. It 
>> almost looks like issuing such advisory is viewed as harmful and 
>> damaging on project "spotless" reputation or something. However in my 
>> view it would show respect to users and understanding that many of 
>> those users might be using it in a way that differs from its creators.
>> It might come as a surprise to some of you, but 95% of Kamailio users 
>> are not reading this and those lists or following Sandro's work in 
>> general. However, if there were a section "Security Advisories" on 
>> kamailio.org <http://kamailio.org> that would be the place to go. And 
>> those users are often not individuals, but companies building their 
>> products and solutions atop of Kamailio.
>> Also properly issued security advisory helps package maintainers, any 
>> linux distro of decent size has its own process to handle and 
>> disseminate those among their own users to update package ASAP. But if 
>> Kamailio chooses to not issue any it basically cuts itself out of that 
>> process.
>> And last but not least, to the remark that I need to step in and fix 
>> things, well I am hardly a person to do that. Too many projects and 
>> too little time, however I also don't think I cannot voice my opinion, 
>> or can I? By the way I know at least one person in the Kamailio 
>> community that might be more fit as a "Kamailio Security 
>> Officer": Olle E. Johansson.  Olle, what's your take on this? Does 
>> this problem warrants security advisory?
>> -Max
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Alex Balashov | Principal | Evariste Systems LLC

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