133 lines
5.7 KiB
Markdown
133 lines
5.7 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:
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- /zncssl.html
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- /english/2015/02/24/znc160-ssl.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](https://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 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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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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- 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 "$SSSLCFFN" | openssl x509 -sha256 -fingerprint -noout
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echo "$SSSLCFFN" | openssl x509 -sha512 -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. 4. added on 2016-01-26._
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There are usually four causes for this. Lets use liberachat as example
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network.
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1. You don't have the `ca-certificates` package installed (`ca_root_nss`
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on FreeBSD), so your system trusts no certificate authority. Install it
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and try again.
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2. You are connecting to wrong address. liberachat's certificate is valid for
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\*.libera.chat, but there are CNAMEs pointing there. If you connect to
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CNAME and the certificate isn't valid for that CNAME, the certificate
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is invalid.
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- You should always connect to `irc.libera.chat`.
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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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4. You have `ca-certificates` installed, but the remote certificate is
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signed by CA that is not included in it. You could try installing
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system updates in case `ca-certificates` have been updated or you will
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have to treat the certificate as invalid until ZNC starts supporting
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it's own CA storage. See (and comment if you encounter this)
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[znc/znc#909](https://github.com/znc/znc/issues/909).
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---
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Section added on 2018-11-10: I have started using the new option to allow
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invalid SSL certificates in some cases as this post is only written with
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clearnet in mind.
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I am on some networks over Yggdrasil or Cjdns which already have E2EE like
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Tor hidden services so as long as they are accessed directly, all benefits
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of TLS are there already and TLS certificates are an additional burden as
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with LetsEncrypt they will change often and LetsEncrypt doesn't support
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any network I mentioned.
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---
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_As I seem to be updating this page more than I originally thought I should
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probably add [this link to changelog here.](https://github.com/Mikaela/mikaela.github.io/commits/master/_posts/2015-02-24-znc160-ssl.md)_
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