what is HTML Smuggling attack? How does it work?  

What is HTML Smuggling attack? How does it work?  

Cybercriminals worldwide are evolving their techniques and coming up with new and improved ways to bypass the defenses and target sensitive information they can leverage for money or political motives, causing massive disruption and impacting reputation.  

Attackers are using advanced phishing techniques to gain access to sensitive information and credentials they can leverage for motives.   

Let us look at another similar method commonly used by attackers – html smuggling. It is one of the modern ways through which attackers deliver malicious payloads to their victims. 

What is html smuggling? 

HTML Smuggling as the name suggests, involves an attacker smuggling malicious code to their target’s endpoint through a unique script tailored to fit into an attachment.  

It evades the existing security mechanisms by disguising itself behind phishing pages that ask users to sign in to Microsoft products like Office 365 and Microsoft Outlook to view fake documents to steal their credentials.  

 It is most used in banking malware campaigns and other specifically targeted cyber-attacks that involve sphere phishing.  

In most of the HTML smuggling attacks, the targeted users receive a sphere phishing email containing a malicious HTML file attachment that when opened, smuggles malicious payload to their device. 

How HTML Smuggling works?  

The attack starts with the attacker sending a phishing email with a malicious HTML attachment that the user opens on his web browser.  When the user interacts with the attachment, it redirects him to a website by decoding a malicious JavaScript Blob that downloads the malware.  

Once the malware is downloaded it assembles on the victim’s device. What makes it dangerous is that it doesn’t pass through any other malicious executables through the network, the attacker undetectably builds it behind an organization’s firewall. 

2024 examples of HTML smuggling attacks 

A recent example of HTML smuggling attacks is the phishing campaigns between March and June 2024, where attackers targeted victims from Asia, North America, and South Europe, specifically from technology, banking, and other financial services sectors.  

These attacks were hosted on Cloudflare Workers®, using phishing pages created on a customized version of Cloudflare’s AitM toolkits. These pages were designed to collect web request metadata, cookies, and tokens when users log to an attacker’s page. It allows the attacker to view all the activities the user performs once they have logged in.  

As per CloudFlare, there was an increase in unique domains from 1000 in Q4 2023 to 1300 in Q1 2024 

HTML smuggling detection and defense tips 

Defending against threats like HTML smuggling requires muti-layered defense, demanding earlier detection mechanisms that could stop the threats at an early stage. It demands endpoint security that can provide defense beyond the perimeter, like a firewall.  

It calls for a defense that can proactively analyze the nature of attachments and links and enable early detection of phishing attempts. For example, if the attachment contains an HTML file with a suspicious script code or JavaScript.   

How can SharkStriker help defend against HTML smuggling?  

SharkStriker’s multi-tenant, open architecture robust security platform STRIEGO offers multiple layers of defense through machine learning based proactive detection of threats across email, endpoints, identities, and cloud apps. It offers a holistic visibility of security posture across the IT infrastructure.  

What makes this defense even more powerful is a team of cybersecurity experts who render human expertise, upgrading the posture with best practices, keeping up with the latest TTPs (Tactics Techniques and Procedures) deployed by threat actors of an evolving landscape.  

Discover the capabilities of proactive tech driven human powered STRIEGO 

To sum it up 

Attackers have found a way around defenses by HTML smuggling that involves unloading malicious payloads through sphere phishing emails with HTML attachments that could fool existing defense mechanisms to steal sensitive, engage in snooping, and other malicious activities upon assembling.   

The most recent case was a series of attacks on multiple victims across Asia, North America, and South Europe.  

An effective defense measure against these attacks is to ensure security at the endpoint level that renders multi-layered defense and proactively analyzes the nature of attachments and links for preemptive detection of HTML smuggling attempts.  

SharkStriker STRIEGO helps defend against threats like HTML smuggling attacks with proactive detection of threats and suspicious activities across multiple vectors be it email, endpoints, identities, and cloud, and centralized visibility of security posture.