Hackers are always coming up with new tricks to lower your defenses and manipulate your trust. You might have been taught to hover over links to see wether they’ll actually take you to the website referenced in the email subject, or to somewhere dodgy. You’ve probably even spotted a few malicious links and prevented unwanted headaches by doing so. Unfortunately, even after hovering over a url and seeing a reputable domain such as adobe.com or google.com, you could still end up getting your credentials stolen or downloading a virus.
Avoiding filters and mitigating hovering
Attackers constantly devise new ways to circumvent spam filters and the increasing awareness of end users. Spam filters easily catch emails containing malicious links that are not obfuscated in any way, such as through redirecting services like bit.ly. At the same time, users are becoming more aware of how to recognize malicious emails with techniques like hovering.
One solution to both of these “problems” (from the attacker's perspective) is to send and host their malicious links and attachments via services that we all know and, most importantly, trust. Microsoft services are prime examples. A spam filter cannot blacklist a domain ending with live.com because doing so would block numerous Microsoft services used in day-to-day business activities. Moreover, a user will trust a legitimate Microsoft domain, making this method quite effective for phishing campaigns, albeit not as common as using some redirecting services.
An attacker can host a malicious website on their own server or on a public cloud hosting service. But these often get taken down quickly, usually within a few days. Even though the lifespan of a phishing email isn’t long, if the attacker's website is taken down immediately then the phishing email is useless.
So, how are these trusted services hijacked by attackers?
Here are a few examples to demonstrate how legitimate sites are used for nefarious purposes.
Legitimate sites such as adobe let attackers host links and attachments on their own site. This means that the malicious content url will end with legitservice.com making it impossible to notice. There is little use in hovering over the link or sometimes even checking the sender domain, unless you are already aware of these tricks. It is harder for the user to blindly trust the good ol' hovering method.
This is why context matters! Most of these links to the legit sites hosting malicious links or files will not be relevant to the context of the email.
Often, the sender of such emails is not the website host, or even anyone related to the email. Typical examples are bank phishes and IT department impersonations. The good thing about these links in most cases is that because they are on a legit service, nothing malicious happens just by clicking the initial link. It’s the malicious site you’re then taken to where things get dangerous. There, whatever you click or download, or whatever credentials you enter, could do harm.
Attack sites using legit services to host malicious links or files stay up markedly longer than sites on regular web-hotels or free hosting services. While researching this blogpost, I found several month-old phishing sites still up and running on legit services, compared to most phishing sites that are taken down in a a day or two.
A few sites where you shouldn’t place your trust just based on the domain:
Any file sharing service
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