If you have a Google account and a stranger sends you a link to a document on Google Drive, think twice before clicking -- it could be a phishing scam designed to harvest your Google credentials.
According to Aditya Sood, architect at Elastica Cloud Threat Labs, the new campaign is reminiscent to one that popped up a year ago, except that this time there are a couple of layers of obfuscation designed to disguise the attack.
Google does have a built-in safety mechanism for its online document storage service, and scans files for malicious code.
But in this particular case, there's no malware to infect a user's machine.
Instead, Google Drive is used to host a simple web page. Documents, spreadsheets, presentations, and photos aren't the only file types that Google Drive supports -- it can even be used to host entire websites.
In this particular case, it's used to host a web page that just mimics the Google account login-screen and harvests user credentials.
"You can share this webpage externally with anyone," said Sood.
Google Users routinely have to log into their Google accounts, and it doesn't feel unusual to be asked for Google credentials, while on a Google-hosted page.
What makes this approach particularly evil is that not only is this fake login page hosted by Google, but it also is protected by Google's SSL certificate.
"It uses the HTTPS that Google uses, and the Google Drive link, which is usually considered legitimate," she said.
Google's own mechanisms are used to distribute the link, so the emails look like real business emails from real people sharing Google documents, not phishing scams, both to end users and to Google's spam filters.
In this particular case, the document being shared is a PDF document, which loaded up after the users had provided their credentials, to help disguise the fact that they were phished.
And since Google uses a single sign-on for multiple services, the attackers can get access to a user's email, calendar, documents, analytics, and any other features they've signed up for.
If they happen to target the administrator of a Google Apps for Business deployment, they can get access to all of a company's communications and other services.
"We reported this to Google through the standard security channel, and then followed up with their security team," Sood said. The phishing campaign is still ongoing, she added, but probably not for long.
"We're are pretty sure that once Google gets on this particular thing, that they will remove it," she said. "But, right now, it's still active, so we're letting people know so at least people won't fall for it."
Meanwhile, there are some warning signs that users could watch out for. For example, the legitimate Google sign-in page says "One account. All of Google." The header on the fake page says "Google Drive. One Storage."
On the fake page, there is a "Create an account" link which just reloads the same page, and if you type in the wrong password it still works -- the attackers don't validate the credentials.