Very small image files that can track user behavior have started to emerge in phishing campaigns, where hackers use them to gather information on their targets, Check Point researchers warn.
These very small image files are designed to send a string of code to an outside website. Usually of only one pixel in size, these images can also be hidden by setting them to the same color as the background of a web page, which allows them to go unnoticed by the user. They can also be used in emails, with the same purpose, and are called tracking pixels because of their small size and obvious purpose.
This information is most often used by marketers to fine tune their advertising, but cybercriminals can also abuse the technique to gather information on cloud-platform components and discover known software vulnerabilities they can exploit in a later attack.
Check Point also explains that phishers can use tracking pixels in their attacks to learn which recipients are most likely to open their scam emails. Phishing attacks that leverage tracking pixels as a surveillance tool have been already observed in the wild, Check Point says.
“Since some scammers retool mass phishing attacks against random users to target high-value enterprise users, scammers are turning to pixel tracking to increase the odds a spear phishing attack will succeed,” the researchers reveal.
The researchers observed tracking pixels in phishing emails in August 2016, when in-place filters prevented the image from loading, which resulted in a red x placeholder image being displayed instead. These small images, Check Point says, threaten privacy in more than emails and web pages.
“For well over a decade, it has been understood that you can utilize tracking pixels in Microsoft Office files like Word documents, Excel spreadsheets and PowerPoint presentations. This works because Office files can link to an image located on a remote Web server. Putting a tracking pixel in an Office document allows you to be able to track a document’s activity as it moves through an organization,” the security firm notes.
While not found to be the direct cause of any specific security breach, tracking pixels are used for their surveillance capabilities in activities that precede attacks against users and infrastructure. The good news, however, is that it’s easy to stay protected.
Enterprises are advised to deploy email and anti-phishing security controls as part of their cloud-security arsenal, as well as to ensure that any software running in a cloud environment is patched at all times. Using web application security to protect any unpatched software should also help prevent intrusion. Looking for anomalous image placeholders when downloading pictures in advertising emails is also a good idea.