To perform HTML smuggling, the QBot malware phishing campaigns utilize SVG image files as a method of distribution. This method creates a malicious installer for Windows that can be run by the user locally.
A Base64 encoded QBot malware installer is reassembled via embedded SVG images that contain JavaScript which can be used to perform this attack. As soon as the target’s browser is opened, the installer will be automatically downloaded and installed.
HTML Smuggling Based on SVG
A phishing email message that delivers the malicious QBot malware can also load other payloads, such as the following:-
- Cobalt Strike
- Brute Ratel
- Ransomware
As the name suggests, HTML smuggling involves encrypting JavaScript payloads into HTML attachments or websites in such a way that they don’t leave any trail behind them.
HTML documents automatically decode JavaScript and execute it when they are opened. Scripts that run locally could be allowed to perform malicious functions, including creating executables that could execute malware.
Threat actors use this method so that they can avoid being detected at the perimeter by the following entities:-
- Security tools
- Firewalls
In a new campaign that was observed by Cisco Talos researchers, QBot phishing emails are used to lure users into opening an HTML document that has been attached to an email reply chain sent using stolen email addresses.
A base64-encoded SVG image is embedded in the HTML of this attachment to hide the malicious code that has been hidden with the aid of an HTML smuggling technique.
Since SVG is a vector image format that is completely based upon XML, it has the capability of including HTML <script> tags and this feature is one of the best legit abilities of this format. While other raster image types like JPG and PNG files don’t come with such abilities.
Here the JavaScript and the SVG format image will be executed and displayed once the HTML document starts loading the SVG file via one of the following tags:-
- <embed>
- <iframe>
In recent years, HTML smuggling attacks have become more common and have proven to be capable of bypassing some security devices.
Primarily what users have to make sure of is that both VBScript and JavaScript execution should be blocked for the downloaded content in order to prevent HTML smuggling attacks from happening.