As a seasoned software engineer, I've delved into numerous projects revolving around email communication, and one recurring hurdle we encounter is the need to monitor email opens. Enter the micro-pixel, a nifty little tool also dubbed tracking pixel or web beacon.
A micro-pixel is a tiny, usually invisible, image (typically 1x1 pixel) embedded in an email that allows the sender to track whether the email has been opened. When the recipient opens the email, the micro-pixel is loaded from a server, which then records the request, indicating that the email has been opened.
Micro-pixels are essentially minuscule, often invisible, images, usually a mere 1x1 pixel in size, stealthily nestled within an email's content. Their purpose? To clue in the sender when the recipient cracks open that email. The moment the recipient triggers the email open, bingo! The micro-pixel sneaks off to a server, triggering a request, and voilà! The sender gets a heads-up that their email has been opened.
How does the magic unfold?
Here's the lowdown: the attacker crafts an image file that's essentially an empty 1x1 pixel. They slip this stealthy pixel into the email content. So, every time an unsuspecting victim opens the email, it unwittingly fires off a request to fetch this pixel image from a specific URL. Sneaky, huh?
Now, the clever part — behind that innocuous URL, the attacker likely has a sneaky server-side script lying in wait. And this script, my friend, is where the magic happens. It can do all sorts of cool stuff, from logging the location and IP of the hapless recipient to executing any instructions the attacker has cooked up.
But here's the kicker: you're not just serving up a bland image file. No, sir! You're serving up a script written in whatever language tickles your fancy, cleverly disguised as an innocent image request. So, while the recipient innocently fetches that pixel image, your script is quietly running in the background, executing all the devious logic you've coded into it. Sneaky, huh? It's like having your cake and eating it too—except in this case, the cake is your malicious script, and the unsuspecting recipient is none the wiser.
0x47, 0x49, 0x46, 0x38, 0x39, 0x61, 0x01, 0x00, 0x01, 0x00, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x2c, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x00, 0x02, 0x02, 0x44, 0x01, 0x00, 0x3b
Oh, and here's a little nugget for you: that snippet of code you see? That's a micro-pixel too, cleverly disguised as a GIF. Crafty, right? And guess what? You can tweak this setup to your heart's content by simply adding custom parameters to the script via GET query parameters in the image's URL. Now, ain't that a nifty trick?
Below an quick and simple script retrieving the user's ip and user-agent :