How does SIM swapping compromise SMS authentication?

Vincent Delitz

Vincent

Created: January 31, 2025

Updated: February 2, 2025

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How Does SIM Swapping Compromise SMS-Based Authentication?#

SIM swapping is a fraudulent attack where cybercriminals take over a user’s mobile phone number by transferring it to a new SIM card. This enables them to intercept SMS-based authentication codes (OTPs) and gain unauthorized access to user accounts.

sim swapping sms authentication risk

How Does a SIM Swap Attack Work?#

  1. Target Identification: The attacker identifies a victim with valuable accounts (e.g., banking, email, crypto wallets).
  2. Social Engineering or Hacking:
  • The attacker impersonates the victim and contacts the mobile carrier.
  • Using stolen personal data (like name, date of birth, or address), they trick customer support into transferring the victim’s phone number to a SIM card they control.
  1. SMS OTP Interception:
  • The victim's phone loses service.
  • The attacker receives all SMS messages, including authentication codes.
  1. Account Takeover:
  • The attacker bypasses SMS-based authentication, gaining full access to sensitive accounts.
  • This often results in identity theft, financial fraud, and data breaches.
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Why Is SIM Swapping a Major Risk for SMS Authentication?#

🚨 Bypasses 2FA Security:

  • Even if users have two-factor authentication (2FA) enabled via SMS, attackers can bypass it and gain access.

💰 Leads to Financial Fraud:

  • Banking, cryptocurrency, and payment accounts are prime targets for SIM swap attacks.

🔓 Weak Carrier Security:

  • Mobile providers lack strong authentication measures, making social engineering attacks successful.

🔄 Hard to Detect in Real-Time:

  • Victims only notice after losing service or when their accounts are already compromised.

How to Protect Against SIM Swapping?#

🔹 Avoid SMS-Based Authentication: Use a more secure method like passkeys or app-based authentication.
🔹 Enable Carrier PIN Protection: Set up a port-out PIN with your mobile provider.
🔹 Monitor for Unexpected Service Loss: A sudden loss of phone service could indicate a SIM swap attack.

Passkeys: The Ultimate Protection Against SIM Swapping#

Unlike SMS OTPs, passkeys use public-key cryptography, making them:
Phishing-resistant
Not tied to phone numbers
Secure against SIM swap attacks

Businesses and users looking to enhance security and eliminate account takeovers should transition to passkeys as a more secure authentication solution.

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