Google Docs Phishing Attack Tricks Unsuspecting Users to Click

NEWS ANALYSIS: A massive phishing attack made use of an API called Google Docs to trick Google users into clicking and becoming victims.

Google secure websites

Phishing attacks are nothing new, but the massive attack on Google Docs that hit the internet on May 3 takes phishing to a new level. 

Users around the world began reporting suspicious emails midafternoon with a Google Docs link, appearing to come from known contacts. The reports surfaced on social media sites including Twitter and Reddit as some users quickly determined that the Google Docs email was in fact a phishing attack.

The official Google Docs Twitter account tweeted at 1:08 p.m. PT that Google was aware of the issue.

"We are investigating a phishing email that appears as Google Docs," the Twitter message stated. "We encourage you to not click through and report as phishing within Gmail."

At 3:20 p.m. PT, the Google Docs Twitter account reported that the phishing email had been addressed.

"We have taken action to protect users against an email impersonating Google Docs and have disabled offending accounts," Google stated. "We've removed the fake pages, pushed updates through Safe Browsing and our abuse team is working to prevent this kind of spoofing from happening again."

Google stated that fewer than 0.1 percent of Gmail users were impacted and only contact data was exposed.

So what happened and how did this phishing attack get through?

Although the attack has widely been reported as a Google Docs phishing vulnerability, to be clear the actual vulnerability was an abuse of Google permissions. The attackers were using a free address from the site and sent an email that made use of an API called "Google Docs" that was requesting user permissions. The Google Docs API phishing attack abused legitimate functionality available via the OAuth protocol to grant permissions.

Granting access to applications for various permissions via OAuth is a common activity, and the Google Docs phishing attack abused that action in a way that should be a major cause of concern for many.

For those who may have been tricked by the attack and clicked on the phishing link, the attacker potentially had access to the victims' Google accounts and contacts. Google recommends that users visit and remove any apps they don't recognize.  

Google has robust security procedures and scanning capabilities, yet somehow an attacker was able to abuse its OAuth API to attack millions of users. This isn't malware or a zero-day vulnerability; it's a worm that abused legitimate functionality.

To be fair, Google responded quickly, but the simple fact is that such an attack should never have happened in the first place. API abuse is an area of security that perhaps has not been heavily scrutinized in the past, but after this incident it clearly should be at Google and around web.

Credit also should be given to CloudFlare, which has taken some criticism this year for leaking information via the so-called Cloudbleed vulnerability. Thanks to the public reports on social media of the attack, CloudFlare was able to notice and block the domains that were being used to spawn and conduct that attack.

It was likely the diligent reports of so many regular users across social media that helped to raise awareness of the Google Docs phishing attack rapidly, leading to its swift resolution. While end users ultimately had to click on the Google Docs phishing email to be exploited, it was other end users, through their vigilant reporting, who helped limit the risk.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.