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The Evolving Threat of Credential Stuffing

Bots' swerve to focus on APIs means businesses must take the threat seriously and take effective action.

Imagine installing a fancy deadbolt lock with a state-of-the-art alarm system for your front door but leaving the back door wide open. No one would do that, right? Yet many companies make a similar mistake with their cybersecurity defenses. They put Fort Knox-like security on the front end of their apps and websites while leaving their back-end critical APIs exposed to the world.

Gartner predicts that by 2022, API abuses will become the most common attack vector resulting in data breaches. "Despite growing awareness of API security, breaches continue to occur," the analyst firm says. When one adds up the total number of breached records over the past few years, more than 50% are exfiltrated via applications and APIs.

It used to be that hackers' preferred method to gain access to online accounts was through user-facing login pages in an account takeover method called credential stuffing. Credential stuffing takes advantage of a common weak point: the tendency of many users to reuse passwords. This makes it easier for an attacker to leverage a list of usernames and passwords stolen from one account and, in a damaging ripple effect, run them against many services.

Cybercriminals execute these brute-force attacks with a huge assist from cheap yet powerful automation tools — specifically bots that hammer sites with various combinations of usernames and passwords over and over until they hit on the right combination and get in.

Like any good drama, a typical credential-stuffing attack plays out in three acts:

  1. The attacker steals credentials from a site or in some cases acquires spilled credentials from a site breach on the Dark Web. It's not uncommon for millions of records to be taken in a single breach.
  1. The attacker uses a botnet to check masses of credentials against multiple accounts and overcome simple detection and mitigation mechanisms by spreading the attack between hundreds or thousands of devices. Entire cybercrime communities have emerged to recommend tactics and sell automated client configuration files dedicated to particular targets.
  1. Upon a successful login, the attacker can take over the accounts and steal personal information such as credit card numbers or reward points. The attacker might also use the account for other malicious purposes, such as sending spam from an email account.

Credential stuffing victims in the last couple of years include Spanish soccer team FC Barcelona, whose Twitter account was hacked and then sent bogus tweets, and Dunkin' Donuts, which warned customers in its DD Perks program that an unauthorized source gained access to some account holders' usernames and passwords.

As more companies get better at locking down their front-end applications and web pages to safeguard against credential stuffing, bad actors have increasingly spotted an opportunity in the back-end APIs and microservices that have tended to be poorly defended. We already see more than half of breaches occurring this way, and the balance will continue to shift more in that direction.

Getting in through an API is appealing to attackers because there are fewer hoops to navigate: Many companies simply are unaware of the huge amount of data they're transmitting via APIs and don’t do a good enough job protecting them.

Add to that the fact that bots comprise an enormous amount of Internet traffic. Forty percent of the 25 petabytes our company processes every month is from bots, and half of that it is for malicious purposes like credential stuffing. Thanks to the public cloud and more sophisticated tools, it has become easier and cheaper for hackers to create and launch ever-more-powerful bots.

Attacks on APIs are a significant threat at a time when they've become the backbone of the software applications that run the digital world. One example is open banking, which is designed to make consumers' lives easier by giving third-party financial services providers electronic access to data from banks and other financial institutions through the use of APIs, with the outside partners then developing new apps and services on top.

So, what can be done?

First, companies simply need to place as high a priority on securing their back-end APIs and services as they have on other parts of their infrastructure. APIs are applications too and a SQL injection is still a SQL injection, regardless if it can be performed through the front end or back end.

Second, major players such as Apple and Google, which have dominant mobile platforms, could bake password management and two-factor authentication (2FA) directly in their respective platforms. These companies have infinite resources to help consumers, and they should. The net result would be a general population with stronger passwords and identity management.

To protect against old-school, front-end credential stuffing, users need to remember to use different passwords for different apps and sites. In the absence of platform-native options, we suggest that individuals use password managers and 2FA solutions. For more serious applications and services, we recommend hardware keys.

Credential stuffing has long been one of the most common types of cyberattacks, but the threat is evolving. Companies need to take the threat seriously and take effective action.

A listing of free products and services compiled for Dark Reading by Omdia analysts to help meet the challenges of COVID-19. 

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