Facebook Google Plus Twitter LinkedIn YouTube RSS Menu Search Resource - BlogResource - WebinarResource - ReportResource - Eventicons_066 icons_067icons_068icons_069icons_070

No, You Aren’t Being Invited to Win a New Car. That’s Spam on Your Calendar

By abusing the automatic event creation feature of integrated email calendars, spammers are finding ways to send you malicious links that are harder to ignore.

Background

In June, researchers at Kaspersky wrote a detailed blog post about phishing tactics involving calendar invite spam, wherein a spammer can automatically add events to your personal calendar, with no interaction on your part, simply by sending you an invitation. All the spammer needs is your email address, either from a stolen or auto-generated list. This isn’t a vulnerability; it’s a function of your calendar working as intended.

Analysis

You are likely already familiar with seeing new events pop up on your calendar as coworkers send invitations to new meetings, regardless of whether or not you’ve seen the email that triggered the invite. This is a feature that calendar apps have enabled by default to make team collaboration swift and efficient. It’s also enabled across both business and personal accounts for all integrated calendars by default. This feature is also becoming more popular with attackers, who are using it for malicious purposes.

As Brian Krebs pointed out in his own blog:

“Calendar invites from spammers run the gamut from ads for porn or pharmacy sites, to claims of an unexpected financial windfall or ‘free’ items of value, to outright phishing attacks and malware lures. The important thing is that you don’t click on any links embedded in these appointments. And resist the temptation to respond to such invitations by selecting ‘yes,’ ‘no,’ or ‘maybe,’ as doing so may only serve to guarantee you more calendar spam.”

Solution

Google is working on a solution for Google Calendar. In the meantime, we strongly advise educating staff to be vigilant and refrain from clicking on unsolicited links. Scammers are banking on the fact that users are likely to be enticed by their messages and will click on the malicious links.

Exchange admins have full control over calendar settings and can ensure that spam invites aren’t automatically added to a user’s calendar, reducing the risk of unwitting clicks on malicious links. Managing this setting should sync with Outlook users within your organization.

Since Apple Calendar doesn’t offer an enterprise version, individual users must manage the settings on their own devices.

Note: Black Hills published a blog in 2017 that details a bypass in Gmail they call MailSniper that ignores user’s attempts to block automatic invites. At the time of publication it seems that Google has yet to fix this flaw.

Identifying affected systems

Because many modern calendar applications are cloud based with little direct organizational control over specific user permissions, the only way we’ve found for an organization to maintain control over user settings against spam is through Exchange Server administration.

As with Apple Calendar, G Suite-dependent organizations must rely on user education to mitigate risk. At present there is no option in the G Suite to manage user calendar settings beyond simple sharing permissions.

Get more information

Join Tenable's Security Response Team on the Tenable Community.

Learn more about Tenable, the first Cyber Exposure platform for holistic management of your modern attack surface.

Get a free 60-day trial of Tenable.io Vulnerability Management.

Subscribe to the Tenable Blog

Subscribe
Try for Free Buy Now

Try Tenable.io

FREE FOR 30 DAYS

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Sign up now.

Buy Tenable.io

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Purchase your annual subscription today.

65 assets

$2,275

Buy Now

Try for Free Buy Now

Try Nessus Professional Free

FREE FOR 7 DAYS

Nessus® is the most comprehensive vulnerability scanner on the market today. Nessus Professional will help automate the vulnerability scanning process, save time in your compliance cycles and allow you to engage your IT team.

Buy Nessus Professional

Nessus® is the most comprehensive vulnerability scanner on the market today. Nessus Professional will help automate the vulnerability scanning process, save time in your compliance cycles and allow you to engage your IT team.

Buy a multi-year license and save. Add Advanced Support for access to phone, email, community and chat support 24 hours a day, 365 days a year. Full details here.

Try for Free Buy Now

Try Tenable.io Web Application Scanning

FREE FOR 30 DAYS

Enjoy full access to our latest web application scanning offering designed for modern applications as part of the Tenable.io platform. Safely scan your entire online portfolio for vulnerabilities with a high degree of accuracy without heavy manual effort or disruption to critical web applications. Sign up now.

Buy Tenable.io Web Application Scanning

Enjoy full access to a modern, cloud-based vulnerability management platform that enables you to see and track all of your assets with unmatched accuracy. Purchase your annual subscription today.

5 FQDNs

$3,578

Buy Now

Try for Free Contact Sales

Try Tenable.io Container Security

FREE FOR 30 DAYS

Enjoy full access to the only container security offering integrated into a vulnerability management platform. Monitor container images for vulnerabilities, malware and policy violations. Integrate with continuous integration and continuous deployment (CI/CD) systems to support DevOps practices, strengthen security and support enterprise policy compliance.

Buy Tenable.io Container Security

Tenable.io Container Security seamlessly and securely enables DevOps processes by providing visibility into the security of container images – including vulnerabilities, malware and policy violations – through integration with the build process.

Learn More about Industrial Security

Get a Demo of Tenable.sc

Please fill out the form below with your contact information and a sales representative will contact you shortly to schedule a demo. You may also include a short comment (limited to 255 characters). Please note that fields with asterisks (*) are mandatory.

Try for Free Contact Sales

Try Tenable Lumin

FREE FOR 30 DAYS

Visualize and explore your Cyber Exposure, track risk reduction over time and benchmark against your peers with Tenable Lumin.

Buy Tenable Lumin

Contact a Sales Representative to see how Lumin can help you gain insight across your entire organization and manage cyber risk.