mikaela.github.io/blog/_posts/2015-02-24-znc160-ssl.md

---
layout: post
comments: true
title: "ZNC 1.6.0 & SSL certificate verification"
category: [english]
tags: [irc, english]
sitemap: false
redirect_from:
  - /zncssl.html
  - /english/2015/02/24/znc160-ssl.html
---

**TL;DR: if you don't verify SSL certificates, don't use SSL!**

ZNC 1.6.0 was released on 2015-02-12 21:05:48Z. It brings multiple
improvements such as taking IP addresses from round-robins randomly instead
of always resolving them into same IP and most notably it actually verifies
SSL certificates.

- [Changelog](https://wiki.znc.in/ChangeLog/1.6.0)

ZNC 1.6.0 also doesn't have option to blindly accept certificates, which
would be stupid, but sadly
[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)
as people are asking how to disable the SSL certificate verification on
\#znc a lot.

Some people even wrote [a patch and scripts to disable the verification.](https://gist.github.com/KindOne-/52cfade7b937ee8b4c37)
This isn't a good idea as patching ZNC can cause all kinds of issues as
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).
See also [contributing (reporting bugs) guidelines of ZNC.](https://github.com/znc/znc/issues/384)

I believe same policy should apply to patching ZNC as to config files,
patch ZNC or edit config file and you will forfeit all support.

## And to the subject

If you don't verify SSL certificates, you only have a false sense of
security as you let anyone between your ZNC and the IRC network. This is
called as [Man-in the middle (or shortly MITM) attack.](https://en.wikipedia.org/wiki/Man-in-the-middle_attack)
There are also people asking for ZNC to trust the certificate for the
first time and then be alerted if the certificate changes. What if the
MITM is there during your first connection attempt and then you are
alerted when the real IRC server gives you wrong certificate?

## So what is the correct way?

- Check the website of your IRC network in case the fingerprints are
  listed on their website.
- Try asking the operators of your IRC network somewhere else if you know
  them (like another network or email).
- This might not be so recommended, but also check the fingerprints from
  multiple locations.

> But the IRC network has hundreds of servers with different certificates!

In this case do what was recommened before ZNC 1.6.0, check some of the
servers that are geographically close to you and use them.

## Checking the fingerprint from multiple locations

I have shell function (which you can find later on this page) which I run
from multiple places:

- my home, Kotka, Finland
- [Kapsi (shell)](https://www.kapsi.fi/english.html), somewhere in Finland
- my VPS, DigitalOcean, London, the UK

```bash
# Get server SSL certificate fingerprint in MD5, SHA1 and SHA256.
# Note that OpenSSL doesn't support IPv6 at time of writing (2015-01-13).
serversslcertfp() {
  SSSLCFFN=$(openssl s_client -showcerts -connect $1 < /dev/null)
  # To see all validity information
  echo "$SSSLCFFN"
  # For getting the fingerprints
  echo "$SSSLCFFN" | openssl x509 -md5 -fingerprint -noout
  echo "$SSSLCFFN" | openssl x509 -sha1 -fingerprint -noout
  echo "$SSSLCFFN" | openssl x509 -sha256 -fingerprint -noout
  echo "$SSSLCFFN" | openssl x509 -sha512 -fingerprint -noout
  unset SSSLCFFN
}
```

I hope this article has helped you to understand the issues with blindly
accepting SSL certificates or at least to understand that _if you don't
want to verify SSL certificates, don't use SSL._

- _Updated on 2015-02-26 10:43Z: just use environment variables in the
  function like suggested by @DarthGandalf on \#znc._

## I am asked to verify fingerprint for network with valid certificate

_Added on 2015-09-03. 4. added on 2016-01-26._

There are usually four causes for this. Lets use liberachat as example
network.

1. You don't have the `ca-certificates` package installed (`ca_root_nss`
   on FreeBSD), so your system trusts no certificate authority. Install it
   and try again.
2. You are connecting to wrong address. liberachat's certificate is valid for
   \*.libera.chat, but there are CNAMEs pointing there. If you connect to
   CNAME and the certificate isn't valid for that CNAME, the certificate
   is invalid.
   - You should always connect to `irc.libera.chat`.
3. There is MITM which is unlikely, but unlikely is not impossible.
   Validating the certificates either by trusted certificates or verifying
   the fingerprints securely manually protect you from this. If MITM is the
   case, you shouldn't connect.
4. You have `ca-certificates` installed, but the remote certificate is
   signed by CA that is not included in it. You could try installing
   system updates in case `ca-certificates` have been updated or you will
   have to treat the certificate as invalid until ZNC starts supporting
   it's own CA storage. See (and comment if you encounter this)
   [znc/znc#909](https://github.com/znc/znc/issues/909).

---

Section added on 2018-11-10: I have started using the new option to allow
invalid SSL certificates in some cases as this post is only written with
clearnet in mind.

I am on some networks over Yggdrasil or Cjdns which already have E2EE like
Tor hidden services so as long as they are accessed directly, all benefits
of TLS are there already and TLS certificates are an additional burden as
with LetsEncrypt they will change often and LetsEncrypt doesn't support
any network I mentioned.

---

_As I seem to be updating this page more than I originally thought I should
probably add [this link to changelog here.](https://github.com/Mikaela/mikaela.github.io/commits/master/_posts/2015-02-24-znc160-ssl.md)_