Strange Bits: HTML Smuggling and GitHub Hosted Malware

[harlan4096]

Sometimes we see odd stuff, like malware that employs a technique called "HTML Smuggling". Also, malware on GitHub seems to be a thing these days.

"That's strange..."

Many important discoveries do not start with a shouting of „Eureka” anymore, as they did in the days of old. Instead, the most intriguing bits of modern research will at some point contain the phrase “That’s strange…”, followed by more prodding and poking and – hopefully – a lightbulb moment. This series that we call "Strange Bits" contains many findings that struck our analysts as odd, either because they do not seem to make any sense at the time or because a malicious program exhibits behaviors that none of us have seen before. Maybe these findings will spark ideas in other fellow researchers – maybe those findings are just what it says on the tin: Strange….

DanaBot loader uses HTML smuggling

This email has an unusual way to store contained malware. The email[1] displays polish text which prompts the user to click on a download link. The translated text says "This file can not be previewed. You can download the file."

The <a> tag for this link has a download attribute with the name of the dropped ZIP archive: dokumentacja_28380.zip[2]. However, the referenced data in the href attribute is not downloaded from a URL but saved as a base64 string using the data URI scheme. This is also called HTML smuggling (thanks to Rich Warren who gave me a hint to the blog post).

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