Abuse of file-sharing services aids phishing campaigns, yet again!

Email has been the lifeblood of enterprise communication and collaboration for decades; there’s simply no doubt about it. Email, however, is also still one of the most effective ways to distribute malware or ransomware, responsible for over 90% of malware deliveries and infections. This is despite the fact that email protection tools have improved and advanced over time.

Today, threat actors leverage free cloud tools, such as hosting providers, file transfer services, collaboration platforms, calendar organizers, or a combination of each, to bypass security measures and disseminate malicious payloads around the world. In this instance, we focus on the Lampion malware campaign, first reported by researchers at Cofense.

What makes this certain phishing campaign more threatening than most, is the use of a legitimate, and in most cases, implicitly trusted service named “WeTransfer”. For the unaware, WeTransfer offers free online file sharing services for users to upload/download content.

Lampion is a known threat strain, first observed back in 2019. In its infancy, it predominantly targeted Spanish demographics, but has since expanded operations across the globe. In 2022, however, researchers have noted an increase in circulation, with some detections exhibiting links to Bazaar and LockBit ransomware campaign hostnames.

The threat actors behind the Lampion malware campaign send phishing emails using hacked business accounts, encouraging end-users to download a ‘Proof of Payment’ mock file hosted on WeTransfer. Its primary objective is to extract bank account details from the system. The payload overlays its own login forms onto banking login pages. When users enter their credentials, these fake login forms will be stolen and sent back to the attacker.

Why do these breaches occur?

With email continuing to be such a vital artery for business operations, it’s no wonder why threat actors apply much of their attention there as one of the most successful vectors for payload delivery.

Then there’s, of course, phishing in its own right as a tactic, technique, and procedure. We, humans, continue to be considered “the weakest links” in cybersecurity, falling for convincing decoys and social engineering lures. Verizon recently backed this trend in their 2022 Data Breach Investigations Report, stating that 82% of breaches are at the hands of humans.

This form of malware is particularly challenging for banking security teams, as the accessing of malicious links are performed through the victim’s system — a trusted device. What’s more, WeTransfer is not the only legitimate service the attackers are using/abusing – they’re also leveraging Amazon Web Services (AWS) resources to host payloads.

Another difficulty lies in the fact that conventional reputational checks performed by security tools may not always be prove to be effective. WeTransfer, as a somewhat-reputable, genuine service, and seemingly-generic AWS-hosted addresses may not necessarily sound off any alarms; at least reputationally on most, if not all, vendor reputation databases.

For this reason, a different, more innovative approach must be considered.

What can be done?

Given these types of threats rely, and thrive on use of external URLs to introduce the payload, remote browser isolation proves to be one of the most effective ways to prevent victim systems from navigating directly to the attacker’s intended content.

Through this method, in the unfortunate event that a victim clicks on a malicious link – i.e. the crafty WeTransfer link in this scenario – a remotely isolated browser session would instantly kick-in to shield the system from any of the forthcoming contents.

How, you ask?

Either based on risky reputational categories (e.g. File Sharing, Peer2Peer, Gambling, etc), URL category, IP address, Domain, or even by matches according to custom created lists, security teams can ensure that if/when their users fall victim to a similar attack, none of the malicious contents from that browser session will ever reach the local device itself – only a visual stream of pixels representing the page

Users can still interact with the site as per normal (as per admin discretion), or they can have functions such as uploads, downloads, clipboard usage, and others blocked entirely. But in this way, the remotely isolated browser session displaying the page shields any of the malicious payloads, cookies, and content from the user and their device.

In doing so, security teams are no longer at the whim of reputational lookups or binary allow/deny policies to spot the wolf in sheep’s clothing.