Multi-Factor Authentication Bypass Led to Box Account Takeover

A vulnerability in Box’s implementation of multi-factor authentication (MFA) allowed attackers to take over accounts without having access to the victim’s phone, according to new research from Varonis.

Because of the vulnerability – which was addressed in November 2021 – an attacker only needed stolen credentials to access an organization’s Box account and steal sensitive data, provided that the account has SMS-based MFA enabled (which has long been proven insecure).

Box, which claims that close to 100,000 companies use its platform, allows users without Single Sign-On (SSO) to further secure their accounts with an authenticator application or using SMS for second-factor authentication.

[ READ: 6 Ways Attackers Are Still Bypassing SMS 2-Factor Authentication ]

When a user tries to log into a Box account, the platform sets a session cookie and then redirects the user to a form where they need to provide either a time-based one-time password (TOTP) from an authenticator app (at /mfa/verification) or an SMS code (at /2fa/verification).

When the user adds an authenticator app, Box assigns a factor ID and, at login, they are required to provide a one-time password generated by the app, in addition to their credentials.

Varonis researchers discovered that an attacker could bypass MFA for accounts where SMS-based MFA is enabled by abandoning the SMS-based verification process and initiating TOTP-based MFA instead.

By mixing the MFA modes, the attacker could access the victim’s account using the correct username and password but then providing a factor ID and code from a Box account and authenticator app the attacker controls.

[ READ: Why Are Users Ignoring Multi-Factor Authentication ]

The issue was that Box did not check whether the user was indeed enrolled in TOTP-based MFA or whether the authenticator app belonged to the user account attempting to log in, the researchers explained.

Thus, the attacker could log into the victim’s Box account without access to the victim’s phone and without the victim being notified of the activity.

“We want to underscore that MFA implementations are prone to bugs, just like any other code. MFA can provide a false sense of security. Just because MFA is enabled doesn’t necessarily mean an attacker must gain physical access to a victim’s device to compromise their account,” Varonis added.

“This was a bug that was identified and addressed prior to the release of the blog post,” Box said in a statement. “We investigate the impact of every bug reported to us and no impact to customers was observed. We’re continually working with the security community and our partners to identify and address potential issues.”

*updated with statement from Box

Related: Why Are Users Ignoring Multi-Factor Authentication

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