The goal of any phishing scam is to make you do something you shouldn’t do. Such is the case with a phishing campaign that utilizes PDF attachments that display login prompts that to many would look legitimate.

If you are a regular reader of BleepingComputer, you know that we like to highlight interesting phishing scams that our readers may encounter. This is to make them aware of them so they don’t fall for scams that stand out from the rest.

Such is the case with the latest phishing campaign found by detection company ReversingLabs and shared with BleepingComputer prior to publication.

What makes this scam stand out is that instead of using fake landing pages, it instead uses fake JavaScript login forms generated directly by the the PDF attachment.

“One such vector that might be overlooked is credential theft via JavaScript-enabled documents,” stated the researchers in their report. “This attack technique doesn’t rely on malicious links or domain spoofing, but on document scripts that yield the same effect”

Tax documents are commonly self-protect with login prompts

If you routinely send tax documents via email for your business, you are probably familiar with password protected PDF documents that are used to protect sensitive tax information.

In this scam targeting German victims, the scammers pretend to be sending you a tax invoice from Amazon and specifically state that you will need to login to your Amazon Seller’s account to view the tax invoice.

If you open the attached PDF file you will be shown a fake login prompt, created using JavaScript, that asks for your Amazon email address and password. Because its a tax document and they specifically stated that a user would have to login to view it, some users may think this is a legitimate request and enter their login credentials.

“The document is asking the reader to log in so they can see the sent tax records. As explained in the email, this screen is to be expected, and typing the credentials into it will show the account summary information. Unusual as it may be, an unvigilant reader might brush it off as a security feature designed to keep their private information safe. But what’s going on behind the scenes?” the researchers explain.

In reality, though, this login prompt is being shown by a JavaScript script that will instead submit any submitted credentials to a long URL located at the http://sellercentral.amazon.de.56U8GTHDGT4U7YWEWE84GTYS.abecklink., which is obviously not the legitimate http://sellercentral.amazon.de.

Once the credentials are entered, the attackers will now have full access to your Amazon account and be able to use it as if they were the legitimate owner.

Protecting yourself from this type of scam

For Phishing scams we normally tell you to examine the URL of any landing pages to make sure they look legitimate. We also advise you to only login to sites at their official domains, rather than through one linked by an attachment.

In this case, the login prompt is being generated to open a protected PDF document, no URLs are being displayed, and you were told that this would happen. 

This is why in addition to checking the landing page URLs you always need to check the sender to make sure they match up with a legitimate domain and one that corresponds with the email you received.

When it comes to tax documents, you should be even more vigilant and reach out to the sender to confirm they sent you sensitive information via email.

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