Google Apps Script Vulnerability Exposes Malware Risks

Research from security firm Proofpoint reveals a mechanism by which Google Apps Script can be used to deliver malware.

Google Safe Browsing Policy

Security firm Proofpoint on Jan. 4 warned of a new attack vector that could enable hackers to abuse Google Apps Script to exploit cloud users.

Google Apps Script is a JavaScript-based language used across the G Suite of applications, including Docs, Sheets, Slides and Forms. The purpose of the language is to help developers and organizations extend functionality in Google's applications, enabling such things as custom menus and functions. 

Proofpoint discovered a flaw with Google Apps Script that could allow an attacker to download malware onto a user's system. 

"Proofpoint research has found that Google Apps Script and the normal document sharing capabilities built into Google Apps supported automatic malware downloads and sophisticated social engineering schemes designed to convince recipients to execute the malware once it has been downloaded," Maor Bin, security researcher at Proofpoint, wrote in an advisory. "We also confirmed that it was possible to trigger exploits with this type of attack without user interaction."

Attackers can take advantage of the Google Apps Script issue to deliver any form of malware or file to victims. According to Proofpoint, it is not aware of the Google Apps Script issue being actively used by attackers.

"We found the vulnerability as part of security research on Google Apps Scripts, not as part of an attack," Bin told eWEEK. "After reporting it to Google, they made mitigations that prevent threat actors from using it."

According to Bin, Google Apps Script now blocks a class of actions known as "installable triggers" that would have enabled script builders to automatically start the installation of a file.

Safe Browsing

Google has a technology known as Safe Browsing that checks URLs against a list of known bad locations for malware. Safe Browsing is directly integrated into Google Chrome as well as Mozilla's Firefox web browser in an effort to protect users against visiting sites with malware. According to Bin, Safe Browsing likely would not have prevented users from being attacked by malware delivered via a malicious Google Apps Script that redirects users.

"Google's Safe Browsing API is effective in protecting end users from a variety of web-based threats including known phishing pages and known sites hosting malware," Bin said. "However, the vulnerability we discovered would have allowed threat actors to host malware on Google Drive itself and deliver the malware from a Google Apps document, limiting the effectiveness of the Safe Browsing technology."

Bin added that sites not on Google's Safe Browsing blacklists are not subject to active blocking via the API.

While Google has now mitigated the specific attack vector disclosed by Proofpoint, other risks associated with cloud documents and data still exist. As is the case with any email link or attachment, Bin advises that users remain vigilant.

"Recipients also should exercise caution clicking even links to Google Docs unless they know or can verify the sender," Bin said.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

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