Mobile phone-based two-factor authentication (2FA) mechanisms are plagued by synchronization vulnerabilities that allow attackers intercept One-Time Passwords (OTPs) and bypass the security of many financial services, researchers say.
In their paper called “How Anywhere Computing Just Killed Your Phone-Based Two-Factor Authentication,” researchers Radhesh Krishnan Konoth, Victor van der Veen, and Herbert Bos demonstrate practical attacks against both Android and iOS devices, showing how a Man-in-the-Browser attack can be elevated to bypass 2FA.
According to the researchers, the increased usage of smartphones and people’s tendency to keep applications synchronized across devices makes phone-based 2FA useless. As soon as an attacker is able to access a user’s computer, the smartphone can be compromised to bypass the security mechanism.
According to the researchers, because 2FA relies on the idea of segmentation to protect against attacks and malware, the process of integrating apps among multiple platforms is negating its benefits and exposes users. They claim that, because of synchronization, once a victim’s computer has been breached, the attacker can engage into Man-in-the-Browser (MitB) attacks and can perform nefarious operations that 2FA should have prevented.
“In this scenario, mobile phone 2FA should guarantee that the attacker cannot perform authorized operations without having also access to the user’s phone. By exploiting certain 2FA synchronization vulnerabilities, however, we show that mobile phone 2FA as used by many online services for secure authentication, including financial institutions, can be easily bypassed,” the researchers say.
The researchers demonstrated the attack by leveraging Google Play’s remote app installation feature, which allowed them to install a specifically crafted vulnerable app on the victim’s registered Android devices. The application, which has to be published in the official store, needs to have already bypassed Google Bouncer. The app is then silently activated and used to hijack OTPs.
The iOS attack, on the other hand, was designed around a new OS X feature called Continuity, which allows users to synchronize their SMS messages between the iPhone and the Mac. In this scenario, should the feature be enabled, an attacker could read SMS messages directly from the infected Mac and doesn’t need control over the iPhone.
The paper also reveals that the synchronization vulnerabilities that allow attackers to bypass 2FA can be exploited in a reliable and stealthy way on Google’s mobile operating system. On iOS, however, the attack relies on SMS synchronization being pre-enabled by the victim, which means that it is not as scalable as the Android attack.
According to the researchers, their SMS stealing app was uploaded to Google Play on July 8, 2015, and was available in the store for two months, until they shared its name and a video demonstration of the attack, although the Android security team was informed months before the initial publication. Apple was notified on the issue on November 30, 2015, but did not provide the researchers with a technical response.
Related: Android Trojan Intercepts Voice Call-Based 2FA: Symantec