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105 lines
4.4 KiB
Markdown
105 lines
4.4 KiB
Markdown
---
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layout: post
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comments: true
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title: "ZNC 1.6.0 & SSL certificate verification"
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category: [english]
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tags: [irc, english]
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redirect_from: /zncssl.html
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---
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**TL;DR: if you don't verify SSL certificates, don't use SSL!**
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ZNC 1.6.0 was released on 2015-02-12 21:05:48Z. It brings multiple
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improvements such as taking IP addresses from round-robins randomly instead
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of always resolving them into same IP and most notably it actually verifies
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SSL certificates.
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* [Changelog](http://wiki.znc.in/ChangeLog/1.6.0)
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ZNC 1.6.0 also doesn't have option to blindly accept certificates, which
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would be stupid, but sadly
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[Quakenet is right about most of people just accepting certificates blindly](https://www.quakenet.org/articles/99-trust-is-not-transitive-or-why-irc-over-ssl-is-pointless)
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as people are asking how to disable the SSL certificate verification on
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\#znc at freenode a lot.
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Some people even wrote [a patch and scripts to disable the verification.](https://gist.github.com/KindOne-/52cfade7b937ee8b4c37)
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This isn't a good idea as patching ZNC can cause all kinds of issues as
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sometimes seen with zncstrap [1](https://github.com/ProjectFirrre/zncstrap/issues/16) [2](https://github.com/ProjectFirrre/zncstrap/issues/18) [3](https://github.com/znc/znc/issues/384).
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See also [contributing (reporting bugs) guidelines of ZNC.](https://github.com/znc/znc/issues/384)
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I believe same policy should apply to patching ZNC as to config files,
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patch ZNC or edit config file and you will forfeit all support.
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And to the subject
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------------------
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If you don't verify SSL certificates, you only have a false sense of
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security as you let anyone between your ZNC and the IRC network. This is
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called as [Man-in the middle (or shortly MITM) attack.](https://en.wikipedia.org/wiki/Man-in-the-middle_attack)
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There are also people asking for ZNC to trust the certificate for the
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first time and then be alerted if the certificate changes. What if the
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MITM is there during your first connection attempt and then you are
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alerted when the real IRC server gives you wrong certificate?
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So what is the correct way?
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---------------------------
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* Check the website of your IRC network in case the fingerprints are
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listed on their website.
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* Try asking the operators of your IRC network somewhere else if you know
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them (like another network or email).
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* This might not be so recommended, but also check the fingerprints from
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multiple locations.
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> But the IRC network has hundreds of servers with different certificates!
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In this case do what was recommened before ZNC 1.6.0, check some of the
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servers that are geographically close to you and use them.
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## Checking the fingerprint from multiple locations
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I have shell function (which you can find later on this page) which I run
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from multiple places:
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* my home, Kotka, Finland
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* [Kapsi (shell)](https://www.kapsi.fi/english.html), somewhere in Finland
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* my VPS, DigitalOcean, London, the UK
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```bash
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# Get server SSL certificate fingerprint in MD5, SHA1 and SHA256.
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# Note that OpenSSL doesn't support IPv6 at time of writing (2015-01-13).
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serversslcertfp () {
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SSSLCFFN=$(openssl s_client -showcerts -connect $1 < /dev/null)
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# To see all validity information
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echo "$SSSLCFFN"
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# For getting the fingerprints
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echo "$SSSLCFFN" | openssl x509 -md5 -fingerprint -noout
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echo "$SSSLCFFN" | openssl x509 -sha1 -fingerprint -noout
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echo "$SSSLCFFN" | openssl x509 -sha256 -fingerprint -noout
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unset SSSLCFFN
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}
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```
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I hope this article has helped you to understand the issues with blindly
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accepting SSL certificates or at least to understand that *if you don't
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want to verify SSL certificates, don't use SSL.*
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* *Updated on 2015-02-26 10:43Z: just use environment variables in the
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function like suggested by @DarthGandalf on \#znc.*
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## I am asked to verify fingerprint for network with valid certificate
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*Added on 2015-09-03.*
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There are usually three causes for this. Lets use freenode as example
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network.
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1. You don't have `ca-certificates` package installed, so your system
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trusts no certificate authority. Install it and try again.
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2. You are connecting to wrong address. freenode's certificate is vaid for
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\*.freenode.net, but some other domains are CNAMEs to it and get
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3. There is MITM which is unlikely, but unlikely is not impossible.
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Validating the certificates either by trusted certificates or verifying
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the fingerprints securely manually protect you from this. If MITM is the
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case, you shouldn't connect.
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