SIM Swapping: Why You Should Never Use SMS for 2FA

You want your funds to be safe, so you turn on two-factor authentication. That's the right move.

You choose SMS-based 2FA because it’s simple. A code shows up, you type it in, done.

While that’s the easiest, it is not the strongest option.

SMS 2FA has a known weakness: your phone number isn’t a secure authentication factor. Carriers can reassign it. Attackers can hijack it. Support teams can be persuaded to move it. If that happens, your login verification codes go somewhere else.

Let’s break down SIM swapping, the security risks of SMS-based two-factor authentication, and the better alternatives offered by KAST so your funds are secure.

What Is SMS-Based 2FA and Why Is It a Security Risk?

When a website sends a one-time password by text message, it’s assuming that your phone number still belongs to you, and your device is the only one that can receive SMS messages.

Neither is guaranteed.

SMS is typically not end-to-end encrypted and relies on telecom infrastructure. If someone gains control of your phone number, they can receive your two-factor authentication codes.

Your password can be strong. If your SMS 2FA can be intercepted, that strength doesn’t help much.

What Is a SIM Swap Attack

A SIM swap attack is when someone convinces your mobile carrier to transfer your phone number to a SIM card or eSIM they control.

Once the SIM swap is complete:

• Your phone loses service.
• The attacker receives your calls and SMS messages.
• Any account protected by SMS-based 2FA becomes vulnerable.

No direct access to your phone or complicated malware is required.

Most SIM swapping attacks rely on social engineering. The attacker contacts your carrier, impersonates you, and requests a new SIM because their phone was “lost” or “upgraded.” If the carrier approves the request, your number is reassigned.

At that point, your two-factor authentication codes go to them.

How a SIM Swap Attack Bypasses SMS Two-Factor Authentication

Here’s how SIM swapping typically plays out:

1. The attacker gathers personal information about you from data breaches, social media, or phishing.
2. They contact your mobile carrier and attempt to pass identity verification.
3. The carrier transfers your number to a new SIM or eSIM.
4. The attacker initiates password reset requests on important accounts.
5. Password reset and 2FA codes are sent via SMS.
6. The attacker uses those codes to access your accounts.

This is why saying “my password is strong” isn’t enough if SMS is your second factor.

If your phone number can be taken over, SMS-based authentication can be bypassed.

What to Use Instead of SMS 2FA: Safer Two-Factor Authentication Methods

You still want two-factor authentication. Just not the SMS version.

Here are better alternatives to SMS-based 2FA.

Authenticator Apps

Authenticator apps like Google Authenticator generate time-based one-time passwords directly on your device. They don’t rely on your phone number or mobile carrier.

Trade-offs:

• If you lose your phone and didn’t save backup codes, account recovery can take longer.
• You need to transfer your authenticator setup before switching or resetting devices.

For most people, app-based 2FA is the best balance of security and practicality.

Hardware Security Keys

Hardware security keys are designed to be phishing-resistant and are not tied to carrier processes, making them extremely difficult to compromise remotely.

However, if you lose the key, you will lose access to your account.

It’s more effort, but its one of the strongest forms of two-factor authentication available.

How to Enable Stronger Authenticators on KAST

Google Authenticator

KAST supports two-factor authentication with Google Authenticator instead of SMS.

To set it up, open the KAST app, go to Security, select Google Authenticator, and toggle it on. You’ll verify with an email code first. Then scan the QR code or paste the setup key into Google Authenticator, and enter the 6-digit code from the app to confirm.

If you ever lose access to your authenticator app, you can use your saved backup codes or request a 2FA reset through Concierge.

Resets require identity verification and typically take 1 to 2 business days, though timing may vary. It’s not instant, and that delay is part of the protection.

Biometric Authentication (Fingerprint and Face ID)

KAST also supports biometric login using fingerprint or Face ID. Biometrics are tied to your physical presence and can't be intercepted remotely like SMS codes.

However, there are also tradeoffs. Biometrics are device-specific. You'll need to re-enable them if you switch devices. If someone has physical access to your device and can mimic your biometric data, they could gain access.

For everyday security, biometric authentication offers a strong layer of protection that's faster than typing codes and more secure than SMS.

The Bottom Line: SMS 2FA Is Convenient but Vulnerable

If you do one thing after reading this, do this:

1. Replace SMS-based 2FA with an authenticator app on any important account.
2. Store your backup codes in a secure place.
3. Keep your device time set to automatic so your codes stay in sync.
4. Never share verification codes with anyone. Not “support.” Not “friends.” No one.

Two-factor authentication is still essential. Don’t turn it off. Just upgrade it.

SMS-based 2FA is vulnerable to SIM swapping, phishing attacks, and phone number hijacking. It works, but it’s one of the easier routes attackers use when they can’t get your password directly.

If you want stronger account security, move away from SMS authentication and switch to an authenticator app or a hardware security key instead.

You’re not being paranoid. You’re removing a weak point.

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