Is SMS 2FA Enough Login Protection?

The "serious attack" against Reddit, disclosed earlier this week, may have only resulted in a limited breach, but Reddit's engineering team and many experts in the security industry believe it should be a strong wake-up call for organizations to bolster their methods of two-factor authentication (2FA). 

According to Reddit's engineering staff, "we suspect weaknesses inherent to SMS-based 2FA to be the root cause of this incident," which exposed old user data and hashed credentials. In its announcement of the scope of the breach, the firm encouraged fellow security professionals to move to token-based authentication. 

That lesson was heard in a loud refrain from security pundits following Reddit's disclosure. 

"While lots of organizations think 2FA is a silver bullet for authentication, it actually isn’t, thanks to weaknesses in mobile networks that allow SMSes to be intercepted," says Leigh-Anne Galloway, cybersecurity resilience lead at Positive Technologies.

The way Reddit was breached is a common attack that takes advantage of unwarranted faith in SMS-based 2FA, she adds. "SMS alone is not enough to constitute adequate defense of customer and employee data," Galloway says. "Two-factor authentication that involves standalone hardware token generators is needed to mitigate the risk of such attacks."

The vulnerabilities of SMS one-time password (OTP) tokens to interception are hardly a secret, says Andy Smith, vice president of product marketing at Centrify. He sees another lesson here about how important it is for security and IT teams to stay abreast of the latest security standards. For example, he points to the fact that the National Institute of Standards and Technologies in its Special Publication 800-63 Guidelines recommends restricting the use of SMS for OTP and advises to completely remove OTP generation via email. 

"Instead, NIST is propagating the use of either application-enabled or hardware-based security keys that are leveraging the FIDO standard," he says.

In fact, hardware-based security keys utilizing FIDO's Universal Second Factor (U2F) standard have been gaining some very high-profile traction from big brands using them both for customers and employees. For example, in January Facebook extended support for U2F to customers that wanted to start protecting their accounts with more secure 2FA methods.

Meantime, just last month Google said it has managed to keep all of its 85,000-plus employees from being phished for over a year since it started making them use U2F-based security keys for logins. The program has been so successful that Google plans on rolling out its own branded security keys to Google Cloud corporate customers.

Nevertheless, some security evangelists believe that the industry shouldn't pile too much on SMS-based 2FA.

"In many cases, it's still better than nothing," says Ilia Kolochenko, CEO of High-Tech Bridge. "Moreover, when most of business-critical applications have serious vulnerabilities varying from injections to RCE, 2FA hardening is definitely not the most important task to take care of." 

SANS senior instructor Jake Williams agrees, stating in a Twitter post that "2FA hard token zealots" should tone it down.

"Stop discouraging orgs from implementing 'good-enough' security," he wrote.

Nevertheless, while SMS 2FA is indeed better than a password alone, it is important for organizations not to be lulled into a false sense of security using it, says Craig Young, computer security researcher for Tripwire's Vulnerability and Exposure Research Team (VERT).

"Although any form of multifactor authentication is a considerable improvement on simple password models, SMS-based verification tokens can be stolen with a variety of well-known techniques, including social engineering, mobile malware, or by directly intercepting and decrypting signals from cell towers," he says.

The interesting aspect of the Reddit breach, Young adds, is that it is not a financial institution, which traditionally is the target for these types of attacks.

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