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.
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.
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.