Deprecation of SMS-based multi-factor authentication (MFA) mode - Zoho Security

Overview of SMS-based OTP MFA mode

The SMS-based OTP MFA method involves the delivery of a one-time password to a user's mobile phone via SMS. The user receives the OTP on their mobile phone and enters it to sign into their account.

SMS-based OTPs offer convenience due to their accessibility; nearly everyone possesses a mobile phone and SMS-based OTPs arrive quickly, allowing for easy and secure authentication.

However, there are some other considerations and security risks that make the SMS-based OTP one of the least preferable options for multi-factor authentication. Hence, we’ve decided to deprecate it as an MFA mode.

Reasons for deprecation

SMS-based OTPs are susceptible to various attacks, including phishing, SIM swapping, and signaling system 7.

Phishing attack: Scammers send fake messages with links to websites that resemble our sign-in page. For example:

Original URL: https://account.zoho.com
Phishing URL: https://accounts.zoh0.com

They trick you into entering your login details and OTPs. If you do, scammers can access your account, putting your personal information and security at risk.

SIM swapping: By knowing your phone number, a scammer can contact your telecom provider's customer service and request to transfer your phone number to a new SIM card, giving them access to your accounts and personal data without your consent.

Signaling system 7 attack: A hacker can spy on you via the cell phone signaling system, where they can listen to calls, intercept text messages, and track your phone's location, leading to serious security risks.

Considering the security threats in SMS-based OTPs and the guidelines on implementing phishing-resistant MFA given by the Cybersecurity & Infrastructure Security Agency (CISA) of the United States government, we deprecated the SMS-based OTP MFA mode.

➤ Current status

Deprecation of SMS-based OTP MFA mode for all users who signed up after January 1, 2024.

➤ Upcoming plan

Migration of existing users and organizations currently enforcing SMS-based OTP MFA to alternate MFA modes.

Alternate MFA modes

If you’re an organization admin, you can set up a different MFA mode for your organization in the security policies. If you’re a personal user, you can go to the multi-factor authentication section at accounts.zoho.com and set up any of the MFA modes described below.

OneAuth (recommended)
Zoho OneAuth is a multi-factor authentication app that you can use to secure your Zoho account as well as third-party accounts, including Google, Facebook, and Microsoft. With OneAuth, you can set up any of the three authentication modes: push notifications, time-based OTPs, and QR codes.
Learn how to set up OneAuth.
OTP authenticator
OTP authenticators are apps you can use to set up MFA for your account. These apps generate new OTPs in duration you set, which you can use to sign in to your account.
Learn how to set up an OTP authenticator.
Security key
A security key is a hardware device that you link to your account to enable multi-factor authentication. Once linked, you'll need to use this key each time you sign in to verify your identity.
Learn how to set up the security key.

If you have any questions, please write to us at support@zohoaccounts.com.

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Deprecation of SMS-based multi-factor authentication (MFA) mode
Overview of SMS-based OTP MFA mode The SMS-based OTP MFA method involves the delivery of a one-time password to a user's mobile phone via SMS. The user receives the OTP on their mobile phone and enters it to sign into their account. SMS-based OTPs offer