The Hidden Risks of SMS-Based Two-Factor Authentication

Written on December 23, 2024

In today’s digital world, securing online accounts is more critical than ever. Cybercriminals constantly develop new tactics to breach systems and access sensitive data, leaving individuals and organizations vulnerable. Two-factor authentication (2FA) has long been championed as a strong defense against unauthorized access, but recent developments highlight that not all forms of 2FA are equally secure.

Recent advisories from the FBI and the Cybersecurity and Infrastructure Security Agency (CISA) ¹ have raised red flags about SMS-based 2FA, exposing its vulnerabilities.

Why SMS-Based 2FA Falls Short

SMS-based 2FA works by sending a one-time password (OTP) to a user’s phone number. While this method is convenient, it is not secure. Here’s why:

Lack of Encryption: SMS messages are transmitted in plain text, making them easy targets for interception by cybercriminals using techniques like SIM swapping or SS7 protocol attacks.

SIM Swapping: In a SIM swap attack, hackers deceive mobile carriers into transferring a victim’s phone number to a new SIM card under their control. This enables the attacker to receive OTPs and gain access to accounts.

Mobile Network Vulnerabilities: The Signaling System No. 7 (SS7) protocol, used by telecommunication networks to manage calls and messages, has known flaws that attackers exploit to intercept SMS messages.

Phishing Attacks: Hackers can trick users into revealing OTPs through sophisticated phishing schemes, bypassing the added layer of security SMS-based 2FA is supposed to provide.

Real-World Example

Recently, a telecom breach exposed non-encrypted messages ², allowing hackers to intercept OTPs sent via SMS. Such incidents have prompted cybersecurity agencies to issue warnings and advise users to migrate to more secure 2FA methods.

Secure Alternatives to SMS-Based 2FA

While SMS-based 2FA is better than no 2FA, more secure options are available:

Authentication Apps: Apps like Google Authenticator, Authy, and Microsoft Authenticator generate OTPs locally on your device, eliminating the risk of interception.

Hardware Security Keys: Devices such as YubiKey or Titan Security Key offer robust protection by requiring physical interaction for authentication.

Biometric Authentication: Some platforms now support biometric methods like fingerprint or facial recognition as an additional layer of security.

Final Thoughts

While SMS-based 2FA has been widely adopted for its convenience, its vulnerabilities cannot be ignored. Transitioning to more secure methods like authentication apps or hardware security keys can significantly enhance your defenses against cyber threats. Staying informed and proactive about emerging risks ensures your online accounts remain protected in an ever-evolving digital landscape.

Take the first step today by reviewing your current 2FA settings and implementing a more secure solution. Your future self will thank you.

Do not use SMS as a second factor for authentication. SMS messages are not encrypted—a threat actor with access to a telecommunication provider’s network who intercepts these messages can read them. SMS MFA is not phishing-resistant and is therefore not strong authentication for accounts of highly targeted individuals. — cisa.gov (PDF)
On December 4, 2024, a top U.S. security agency confirmed reports that foreign actors, state-sponsored by the People’s Republic of China, infiltrated at least eight U.S. communications companies, compromising sensitive systems and exposing vulnerabilities in critical telecommunications infrastructure. This was part of a massive espionage campaign that has affected dozens of countries. — docs.fcc.gov (PDF)