The other week I wrote about a plugin I made that lets you syndicate content from a Known site to an IRC channel.

Since folk using other platforms expressed an interest, I thought I’d quickly write down how to do it for the other indieweb folk out there.

Getting started

Writing content to an IRC channel is actually pretty straightforward, I’ll get onto the specifics of what you need to do in a moment, but your first step is to collect necessary information.

At the very least you’ll need:

  • Server details: Server (e.g., Port (e.g 6667, or better, 6697 for TLS)
  • The channel you want to post to (e.g. #indiewebcamp)
  • The nickname to use (and password if your nick is protected by nickserv)

Collect that information (or hard code it if it’s just for you), you’ll need it later.

Making a post

Posting some content to the channel after this is fairly straightforward. Obviously, if you want to persist on the channel you’ll need to start thinking about implementing a proper bot, but a single posting doesn’t need to get into that.

The basic protocol is:

  • Connect to the server on the given port, and I strongly suggest you use TLS.
  • Greet the server by sending the following:

    All the *username* bits in the first line are actually meant to be your username, fullname and nickname. For brevity, because I wasn’t writing a full client, I just used the same thing.

  • Wait for response from server. At this point the server will spit back some information about the server, and may ask you some questions. You *should* parse that intelligently, but I couldn’t be bothered, so I just wait a few seconds.
  • If you need to send a password to the nickserv, do so now:

    Wait for response (or a few seconds) as before.

  • Join your channel:

    and wait for response.

  • Post your message:

    and wait…

  • Quit:

    and close your connection.

If you want to experiment with this before you start coding, you can connect and do the whole exchange by hand via telnet/telnet-ssl, e.g:

Some gotchas

All in all, posting to an IRC channel is pretty straightforward, however there are a few things that can trip you up.

  • Don’t be too fast: The main issue is that if you just open the connection and splurt your commands, you likely won’t get anywhere. The server will respond, and will expect you to listen to what it says. As I said above, the best thing is to read and process this response intelligently, but you can of get away with just waiting a few seconds… obviously YMMV.
  • Nickname collisions: The above code doesn’t handle a situation where the nickname is already active on the network. I sidestep this issue by using a different username than my regular IRC handle for my syndication user, and to use nickserv to guard it. If you don’t want to take that approach you’re going to need to do something else, like parse the server response to detect the problem and present alternate nicks.

Happy syndicating!


On the Indiewebcamp wiki, there’s a page discussing HTTPS, the support for which is strongly recommended. As I’ve mentioned previously, at this stage all non-encrypted communication forms (including traditional port 80 HTTP) should be considered deprecated and dangerous.

Indieweb compatible sites are encouraged to get a higher level as possible, and thanks to some prodding, I’ve finally moved both this blog and my feed over to HTTPS only, with HSTS and forward secrecy.

This got me thinking, perhaps it would be worth adding a “Level 7” (or perhaps Level 6.5) to this, and to suggest that Indieweb sites should also be made available as .onion hidden services on Tor?


  • Anonymity. Would go a large way towards protecting communication metadata (who know’s whom), which is a goal we should move towards in a world of endemic selector based surveillance.
  • Encryption. Traffic within the tor network is end to end encrypted, and there is some discussion of whether this renders HTTPS unnecessary.


  • Tor has nothing to do with HTTPS, although it is encrypted. However, the HTTPS levels page seemed a good place to put the suggestion.
  • Could be seen as endorsing one service. Tor is Free software and is pretty much the only game in town when it comes to anonymity networks, but does that constitute a silo? Probably not, but is a point for discussion.
  • No certificates for .onion. There are currently no certificate providers available for .onion domains. But, this may not be a problem.

Anyway, just mooting this as a point for discussion.

In this post I’m going to discuss a potential attack, using a common method of implementing webmention comments on a site, that can allow an attacker to obtain visitor information from a third party site, and to possibly launch drive-by attacks.

This came about from a discussion related to retrieving non-TLS protected resources from a TLS protected site, and it got me thinking that the problem went a little deeper.

The Attack

A common way of handling webmentions on an Indieweb site, such as those powered by Known, is as follows:

  1. Alice writes an comment on her site, and references Bob’s post
  2. Alice sends a webmention to Bob’s site referencing the URL of her comment, and the post she’s referring to.
  3. Bob’s site retrieves Alice’s comment & parses it for Microformats markup
  4. If all things check out, Bob’s site then renders the comment using text, profile url and profile icon information obtained from Alice’s site.

It is step 4 that’s the problem here.

Typically, when the webmention is parsed and rendered by Bob, the site software will attempt to construct a nice looking comment. To do this, the site software will typically render an avatar icon, together with a user name, next to the comment. This information is obtained by parsing MF2 data from Alice’s site, and while the Webmention spec says that content should be sanitised for XSS etc, profile icons are often overlooked – a URL is fairly innocuous, so it’s generally just dropped into an img tag.

Now, if Alice was evil, she could, for example, configure her server to send “in the past” cache headers when her server served her avatar. This would mean that her server logs would then start collecting some detailed traffic information about the visitors of the page she webmentioned, since every visitor’s browser would retrieve a new copy of her profile icon.

She could, if she was very smart (or was a well funded government agency sitting on a whole bunch of zero day browser exploits) serve specially crafted content designed to trigger a buffer overflow in a specific visitor’s browser at this point.

Worse, she could do this even if the entire site was protected by TLS.


The simplest way to prevent this kind of exploit is not to render profile icons from webmentions. This is, however, a sub-optimal solution.

My current thinking is that Bob’s site (the site receiving and rendering the webmention) should, when receiving the webmention, fetch and cache the profile icon and serve it locally from his server.

This would prevent Alice from performing much in the way of traffic analysis since her server would only be hit for the original request. If you server re-samples the image as well (to enforce a specific size, for example) then the process would likely do much to strip any potential hidden nasties embedded in the file.

There is a DoS potential to this, but techniques for mitigating DoS for webmention/MF2 parsing have already been discussed in the Webmention spec.

Anyway… thoughts?