Wednesday December 14, 2022

Issue Summary:

On December 14, 2022 from 4:30 AM PST to 9:00 AM PST, we received reports from customers who were unable to receive SMS 2FA codes to log into Slack.

We discovered that the Slack queue on a third party 2FA service, and associated outgoing SMS message errors, were growing at a high rate. Customers who had enabled 2FA via SMS were affected in at least India, China, US, Brazil, and Argentina. We identified that a majority of traffic was coming from bad actors, whose requests led to unusually high volume for our queue.

We prevented these individuals from accessing Slack, while our 2FA service provider implemented a change to further mitigate strain on our queue. These actions resolved the issue for all impacted customers.

Note: This summary has been edited since its initial posting to better align with Slack's communication guidelines.

5:25 PM PST

The issue with two-factor authentication codes via SMS has been resolved. We apologize for any inconvenience.

11:36 AM PST

We're still investigating the issue with users being unable to receive two-factor authentication codes via SMS. We don't have additional information to share just yet. We'll be back shortly with another update.

8:53 AM PST

Some users are currently unable to receive two-factor authentication codes via SMS. We're looking into this with our service provider and hoping to restore functionality again soon.

We apologize for the disruption and we'll share more updates once we have additional information.

7:48 AM PST