Posts tagged ‘coding’

Zombies banging at the WordPress door

Zombies are impossible to avoid in this day and age, even (maybe especially) online. Anyone who maintains a publicly accessible server and pays even passing attention to their security logs can attest to the repeated brute force login attempts for everything from SSH to WordPress admin panels. Having a strong SSH password, disabling root logins, and changing the default port works wonders, but doesn't help with my WordPress installation, which is where I most often get hit these days.

In the past, these naive attacks were fairly easy to block using tools like fail2ban or using plugins like Limit Login Attempts, which put IP addresses on a blacklist for too many failed login attempts. Unfortunately, of late it seems like the crackers have caught on, and are now bringing the full force of the zombie hordes to bear: each zombie computer only tries logging in to a particular website once, preventing an IP blacklist from having any effect.

Thus, I've had to resort to more drastic action: IP whitelists by placing the following code in the .htaccess file of my WordPress directory:

<Files wp-login.php>
order deny,allow
deny from all
allow from
</Files> should obviously be replaced with your IP address unless you only access WordPress Admin from the server itself (either directly or through a proxy like Socks5). I have a dynamic IP address, but now use a Socks5 SSH tunnel for working on WordPress. Anyone else trying to login will now get a 403 forbidden page, not only adding to my peace of mind, but also saving me the processing time and bandwidth of serving up the login page to would-be crackers. 😀

GNU screen / Bash: start commands in interactive sessions

I run nearly everything from the terminal, including my mail client (mutt), music player (cmus), custom simulation software (Python/Matlab/C), and some hacked together daemon-like mail and server scripts—my browser (Firefox) is the only always-on GUI application. Thus, GNU screen is an essential tool in my workflow, since it allows for easy multiplexing and detaching of sessions.

One of its many features is the ability to start multiple sessions and automatically run commands in each of them. This isn't necessary for my server and workstation, since I just run screen persistently. However, my MacBook Pro is a different story, and not having to start up each program individually is a great convenience. The canonical way to do so is through creation of an alternate screenrc

# $HOME/.screen/startuprc
source $HOME/.screenrc
screen -t cmus 0 cmus
screen -t mutt 1 mutt
screen -t bash 2
screen -t custom_title 9

and to then invoke screen -c ~/.screen/startuprc.

This works great with stable programs like cmus and mutt, but I oftentimes need to restart my hacked together scripts, maybe after a crash or if I just want to tweak the code. Unfortunately, as set up, once an automatically started program finishes running, screen (correctly) exits the session. Starting up a new session each time can get a bit old.

The easiest solution I found was to create a custom Bash rcfile for each program, which would first source ~/.bashrc and then run the command at hand (e.g. This way, an interactive Bash session remains after exiting the program.

# $HOME/.screen/startuprc
source $HOME/.screenrc
screen -t cmus 0 bash --rcfile $HOME/.screen/cmus_rcfile
screen -t mutt 1 bash --rcfile $HOME/.screen/mutt_rcfile
screen -t bash 2
screen -t custom_title 9 bash --rcfile $HOME/.screen/custom_script_rcfile

This is almost sufficient, but there's still one quirk left. Because Bash is running the script from an rcfile, it doesn't store the command in its history buffer. A minor thing, to be sure, but it means I can't use the four-keystroke sequence ctrl-C, <up>, <enter> to restart programs. Luckily, Bash provides a means of deliberately inserting commands into history without running them, so the simple addition of history -s "command" to the appropriate rcfile fixes that:

# $HOME/.screen/custom_script_rcfile
history -s ""

And that's it! I'd love to hear if anyone has come up with a more elegant solution. For now though, the above provides everything I need, and is relatively simple to setup. Happy hacking!

A simple Chrome extension to remove external URL mangling by Facebook

Update 2012-12-09: Facebook changed their URI mangling code, so this probably won't work as written anymore. However, a similar scheme should still work if you take the time to read the FB source code to figure out how to remove the new mangling code. (I no longer actively use FB, so I haven't updated the extension).

One of the thing's that's been irritating me lately about Facebook is it's habit of mangling the URLs of all links going away from the site. The status bar displays the correct URL, for instance

but upon actually clicking the link, some clever javascript substitutes

which is on Facebook's server, but then immediately redirects the user to XKCD. Facebook is thus able to track the links clicked, which presumably lets them better personalise the News Feed content.

This shouldn't surprise anyone, as most (if not all) of the major Internet players do some sort of click tracking, and Facebook in particular is well known for its stance on privacy. I'm not too bothered about it from a privacy standpoint, as I choose to give away a lot more personal information to Facebook anyways. Indeed, other net giants Google and Yahoo use a similar technique for all of their search results1, and Bing is smart enough to track clicks without resorting to link mangling. Click tracking is an integral part of online advertising, and since I'm using free services, I won't fault a profit-making company for employing it.

However, the difference is that the Facebook's links don't work properly when copied and pasted from one browser instance to another2. They instead send you to a redirection page requiring a manual click through, which is all right every so often but irritating in repetition.

Facebook Redirection Page

Facebook Redirection Page

Luckily, modern browsers come with a wide array of tools, and in this post, I'll be using a simple Chrome extension3 to remove the link mangling, allowing me to copy and paste my links in peace. It also has the side effect of possibly keeping Facebook from tracking my external clicks, but that's another matter entirely4

I should warn you at this point that there will be some minimal amount of coding involved, but if you are using multiple browser instances, than I'll assume you're up to the task. First, you'll need to create a folder to contain the extension files, say FacebookLinkDeMangler. In that folder, create manifest.json as

// manifest.json
// Describes the extension & tells Chrome what scripts to run
  "name": "Facebook Link De-Mangler",
  "version": "0.1",
  "description": "Disables Facebook external link mangling",
  "content_scripts": [
      "matches": ["*://**"],
      "js": ["jquery-1.6.2.min.js","main.js"],
      "all_frames": true

The first couple of lines are just description; content_scripts is where actual instructions go. In this case, we're telling Chrome that for all pages on Facebook, run jquery-1.6.2.min.js and main.js.

Of course, those two files need to exist for the extension to function properly. First, go and grab yourself the latest version of JQuery, which is a free Javscript library enabling all sorts of cool tricks5. Then just create main.js:

function modifier()
// The following line is optional and will highlight all external links in yellow
$("a[href][onmousedown^='UntrustedLink.bootstrap']").css({'background-color': 'yellow'});

intID = setInterval("modifier()",5000); 

All of Facebook's links that go to external pages call UntrustedLink.bootstrap in order to alter the URLs when the mouse is clicked on it. The modifier function gets rid of the onmousedown attribute, so the link remains unmangled. It runs every 5 seconds, which is necessary because page content loads dynamically in Facebook, and not just once.

And that's it; I told you the coding was minimal. Of course, the new extension needs to be loaded. To do that, go to the Google Chrome extensions manager. If there's a "+" next to "Developer Mode", you'll need to expand that. Then just "Load Unpacked Extension" and direct Chrome over to the folder you saved the files in (e.g. /path/to/FacebookLinkDeMangler). Now for the final step: copy and paste links from Facebook to your heart's content. That's all folks!

  1. To be fair, Google only mangles links when a user is logged in.
  2. I oftentimes have multiple instances of Chrome and Firefox running to be simultaneously signed in under different accounts.
  3. For those using Firefox, it should be trivial to write a similar script using Greasemonkey, though I haven't tested it myself.
  4. Facebook could also be doing something similar to what Bing does, and do remember that any time you visit a site that's enabled Facebook's Social Plugin, your visit is probably sent to their servers.
  5. If it's a later version of JQuery, the filename in manifest.json will obviously need to be updated to match.