Make Sure You are Protected Against Google Calendar Phishing Attacks

A Google Calendar phishing campaign is being conducted that abuses trust in the app to get users to click malicious hyperlinks.

Cybercriminals are constantly developing new phishing tactics to convince end users to click links in emails or open email attachments. These campaigns are often conducted on organizations using Office 365. Campaigns are tested on dummy Office 365 accounts to make sure messages bypass Office 365 spam defenses.

Messages are carefully crafted to maximize the probability of an individual clicking the link and the sender name is spoofed to make the message appear to have been sent from a known and trusted individual.

Businesses that implement email security solutions that incorporate DMARC authentication can block the vast majority of these email spoofing attacks. Office 365 users that use a third-party anti-phishing solution for their Office 365 accounts can make sure malicious messages are blocked. Along with end user training, it is possible to mount a solid defense against phishing and email impersonation attacks.

A new phishing tactic is being used in an active campaign targeting businesses which achieves the same aim as an email-based campaign but uses a personal calendar app to do so.

Phishing campaigns have one of two main aims – To steal credentials for use in a further attack or to convince the user to install some form of malware or malicious code. This is most commonly achieved using an embedded hyperlink in the email that the user is urged to click.

In the Google Calendar phishing attacks, events are added into app users’ calendars along with hyperlinks to the phishing websites. This is possible because the app adds invites to the calendar agenda, even if the invite has not been accepted by the user. All the attacker needs to do is send the invite. As the day of the fictitious event approaches, the user may click the link to find out more. To increase the likelihood of the link being clicked, the attacker sets event reminders so the link is presented to the user on multiple occasions.

This attack method is only possible with Google Calendar in its default setting. Unfortunately, many users will not have updated their settings after installation and will be vulnerable to Google Calendar phishing attacks.

To prevent these attacks, on the desktop application settings menu click on:

Event Settings > Automatically Add Invitations

Select the option, “No, only show invitations to which I’ve responded.”

Navigate to “View Options” and ensure that “Show declined events” is not checked.

