A CAPTCHA phishing scam has been detected which is being used to trick users into downloading a malicious file that intercepts multi-factor authentication codes on a user’s smartphone. With the codes, hackers can perform a more extensive attack and gain access to a much wider range of resources such as email and bank accounts.

When a visitor lands on the phishing page, a check is performed to determine what device is being used. If the user is on an Android device, a malicious APK file is downloaded to their device. Any other platform will receive a zip file containing malware.

A fake version of the familiar Google reCAPTCHA is displayed on the phishing page. It closely resembles the legitimate version, although it does not support sound and the images do not change when they are clicked. The fake reCAPTCHA is housed on a PHP webpage and any clicks on the images are submitted to the PHP page, which triggers the download of the malicious file. This campaign appears to be focused on mobile users.

On an Android device, the malicious APK intercepts PIN codes from two-factor authentication messages, which allow the attackers to gain access to the user’s bank account. With these PIN codes, an email account can also be compromised, which would allow further accounts to be compromised by requesting password resets.

A successful attack could see several accounts used by an individual subjected to unauthorized access. Businesses are also attacked in a similar manner. Successful attacks on businesses could give the attackers access to huge volumes of sensitive company data and even infrastructure resources.

This method of delivering malware is nothing new and has been around since 2009. A CAPTCHA phishing campaign was detected in February 2018 attempting to download a malicious file, and a similar campaign was run in 2016.

A method of attack is adopted for a while then dropped. While it is possible to prepare the workforce for phishing attacks such as this through training, security awareness training alone is not enough as tactics frequently change, and new methods of attack are frequently developed.

As this attack shows, two-factor authentication is far from infallible. In addition to this method of obtaining 2FA codes, the SS7 protocol used to send SMS messages has flaws that can be exploited to intercept messages.

Security awareness training and 2FA are important, but what is required on top of these protections is a powerful anti-spam and anti-phishing solution. Such a solution will block phishing emails at the gateway and make sure they are not delivered to inboxes.

It is important to choose a solution that provides protection against impersonation attacks. Many phishing campaigns spoof a familiar brand or known individual. A solution that incorporates Domain-based Message Authentication, Reporting & Conformance (DMARC) will help to ensure that the sender of the message is genuine, by performing checks to make sure that the sender of the message is authorized to send messages from that domain.

Most anti-phishing solutions incorporate an anti-virus component that scans all incoming attachments for malware and malicious code, but cybercriminals are using sophisticated methods to evade detection by AV solutions. Files may include malicious code that is hard to detect. A sandbox is therefore required to execute suspicious attachments in a safe environment where they can be monitored for malicious activity. By testing attachments in the sandbox, malicious files can be identified and more genuine emails and attachments will arrive in inboxes.