"The amount of critical and private data that web browsers mediate continues to increase, and naturally this data has become a target for criminals. In addition, the webís advertising ecosystem offers opportunities to profit by manipulating a userís everyday browsing behavior," the researchers noted in the paper detailing their findings.
"As a result, malicious browser extensions have become a new threat, as criminals realize the potential to monetize a victimís web browsing session and readily access web-related content and private data."
To analyze the extensions, the researchers used Hulk, a dynamic analysis system of their own making, which flushes out the extensions' malicious behaviour.
"First, Hulk leverages HoneyPages, which are dynamic pages that adapt to an extensionís expectations in web page structure and content," they explained. Second, Hulk employs a fuzzer to drive the numerous event handlers that modern extensions heavily rely upon."
Among the malicious extensions they found, some perpetrated affiliate fraud and credential theft, others performed ad injection or replacement, and others still abused social networks for spamming.
The researchers also offered a set of recommendations that would prevent some of these attacks, and they hope Google will implement them.