Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.


01:45 PM
Connect Directly

New 'Duri' Campaign Uses HTML Smuggling to Deliver Malware

Researchers who detected the attack explain what businesses should know about the HTML smuggling technique.

A new attack campaign is using HTML smuggling and data blobs to deliver malware onto victim machines while evading network security solutions including sandboxes and legacy proxies.

This particular attack, dubbed Duri by the Menlo Security researchers who discovered it, was first detected in early July of this year and is currently active. The team identified a user's visit to a website and noticed the subsequent file download was flagged as suspicious and then blocked. Further analysis revealed the file was downloaded through HTML smuggling.

The goal of HTML smuggling is to leverage HTML5/JavaScript features to deliver file downloads. Attackers can deploy the download using Data URLs on the client device, or they can create a JavaScript blob with the correct MIME-type, which results in a download on the target device.

"With Duri, the entire payload is constructed on the client side (browser), so no objects are transferred over the wire for the sandbox to inspect," researchers state in a report. In this case, they say, attackers were seen using the JavaScript blob technique to smuggle malicious files via the browser onto the target's endpoint.

How this unfolds: When a user clicks a link, there are multiple redirections before that person lands on an HTML page hosted at duckdns[.]org. This prompts a JavaScript online, which then initializes data for a blob object from a base64 encoded variable. A .zip file is constructed from the blob object and downloaded onto the endpoint. The user needs to open and execute the .zip file, which contains an MSI file and indicates it's a Microsoft Windows installer.

Researchers note the malware deployed is not a new threat. However, they aren't at a point where they can reveal the malware family and/or who might be behind this attack campaign.

"The malware that Duri downloads is not new," they say. "According to Cisco, it has previously been delivered via Dropbox, but the attackers have now displaced Dropbox with other cloud hosting providers and have blended in the HTML smuggling technique to infect endpoints."

The HTML smuggling technique is also not new or novel, says Krishnan Subramanian, a security researcher at Menlo Labs. This is simply the latest instance of an attack technique that proves effective for increasingly sneaky intruders who want to bypass security products.

"It's not taking advantage of any security weakness or vulnerabilities – that's the premise of this attack," Subramanian explains. "It makes use of the legitimate features of HTTP protocols, specifically HTML5 and JavaScript APIs, to sneak malicious files."

Traditional network security tools, such as proxies, firewalls, and sandboxes, depend on the transfer of objects over the wire to flag malicious activity. A sandbox may be instructed to extract certain file objects objects – for example, .exe or .zip – to be detonated and further analyzed. HTML smuggling allows attackers to bypass the content inspection layers that identify malicious file downloads.

Researchers anticipate attackers will continue to rely on HTML smuggling as they adjust their tactics to bypass security tools, forcing victims to depend on a "detect-and-respond" approach to catch up.

"These types of attacks demonstrate the threat landscape is becoming more and more complex," Subramanian says.


Kelly Sheridan is the Staff Editor at Dark Reading, where she focuses on cybersecurity news and analysis. She is a business technology journalist who previously reported for InformationWeek, where she covered Microsoft, and Insurance & Technology, where she covered financial ... View Full Bio

Recommended Reading:

Comment  | 
Print  | 
More Insights
Newest First  |  Oldest First  |  Threaded View
7 Old IT Things Every New InfoSec Pro Should Know
Joan Goodchild, Staff Editor,  4/20/2021
Cloud-Native Businesses Struggle With Security
Robert Lemos, Contributing Writer,  5/6/2021
Defending Against Web Scraping Attacks
Rob Simon, Principal Security Consultant at TrustedSec,  5/7/2021
Register for Dark Reading Newsletters
White Papers
Current Issue
2021 Top Enterprise IT Trends
We've identified the key trends that are poised to impact the IT landscape in 2021. Find out why they're important and how they will affect you today!
Flash Poll
How Enterprises are Developing Secure Applications
How Enterprises are Developing Secure Applications
Recent breaches of third-party apps are driving many organizations to think harder about the security of their off-the-shelf software as they continue to move left in secure software development practices.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
PUBLISHED: 2021-05-13
An improper access control vulnerability has been reported to affect earlier versions of Music Station. If exploited, this vulnerability allows attackers to compromise the security of the software by gaining privileges, reading sensitive information, executing commands, evading detection, etc. This ...
PUBLISHED: 2021-05-13
A command injection vulnerability has been reported to affect certain versions of Malware Remover. If exploited, this vulnerability allows remote attackers to execute arbitrary commands. This issue affects: QNAP Systems Inc. Malware Remover versions prior to This issue does not affect: QNAP...
PUBLISHED: 2021-05-13
An improper authorization vulnerability has been reported to affect QNAP NAS running HBS 3 (Hybrid Backup Sync. ) If exploited, the vulnerability allows remote attackers to log in to a device. This issue affects: QNAP Systems Inc. HBS 3 versions prior to v16.0.0415 on QTS 4.5.2; versions prior to v3...
PUBLISHED: 2021-05-13
An Authentication Bypass vulnerability in the SAML Authentication component of BlackBerry Workspaces Server (deployed with Appliance-X) version(s) 10.1, 9.1 and earlier could allow an attacker to potentially gain access to the application in the context of the targeted user’s acco...
PUBLISHED: 2021-05-12
Use After Free vulnerability in nfc sockets in the Linux Kernel before 5.12.2 allows local attackers to elevate their privileges. In typical configurations, the issue can only be triggered by a privileged local user with the CAP_NET_RAW capability.