Sentry MBA Uses Credential Stuffing to Hack Sites

Shape Security warns of the growing threat of the hacking tool, which is able to bypass many modern IT defenses.

data breaches

Cyber-attackers use a lot of different tools, but one in particular is becoming increasingly effective as the collateral damage from Website breaches spreads. Shape Security today is warning about the dangers of the black market tool Sentry MBA (Modded by Artists) that is being used in widespread attacks known as credential stuffing.

"The basic idea behind credential stuffing is that hackers are moving away from doing brute-force attacks, since the security industry is doing a reasonable job of blocking those attacks," Shuman Ghosemajumder, vice president at Shape Security, told eWEEK.

With a brute-force attack, a hacker tries all possible combinations for an eight-digit password and eventually discovers the correct one. However, thanks to widespread use of password input restrictions, such that many sites and services will now block a user after three failed log-in attempts, brute force has fallen out of favor, Ghosemajumder said.

Instead, there is a growing trend that Hewlett Packard Enterprise (HPE) has labeled collateral damage, where lists of credentials from compromised third-party sites are used to attack other sites. When attackers obtain lists of user credentials that were gleaned from other sites, they still need to figure out which credentials are valid and where else they can be used, he said. Attackers are increasingly using automation techniques to determine the tiny subset of credentials that can be reused on various sites, which is where Sentry MBA comes into play.

There are many credential stuffing tools, though in recent months Sentry MBA has emerged to become the most popular, according to Ghosemajumder. Among the reasons for its popularity is that it has a nice user interface and is a modular tool, he said. The modularity abstracts the credential stuffing functionality from the specific details of the Website a hacker is trying to attack. By way of Sentry MBA config modules, an attacker is able to tailor an attack to a specific Website, bypassing the specific defenses, including third-party security tools that may be in use on a targeted Website.

As an example, if a site serves a CAPTCHA that shows up whenever the site detects anomalous traffic, Sentry MBA can use the Death by Captcha API, which is a service built by different cyber-criminals to get around any CAPTCHA system, including Google's re CAPTCHA service.

Shape Security's research found that in a one-week period in December 2015, attackers made 5 million log-in attempts at a Fortune 100 business-to-consumer (B2C) Website by way of Sentry MBA. In January, over a two-day period, Shape Security saw a Sentry MBA attack with more than 20,000 total log-in attempts against a large retailer. Information on how to use Sentry MBA isn't hidden on the dark Web either. In fact, a simple search on YouTube will find dozens of how-to videos.

"Even though this [Sentry MBA] is the most widespread credential stuffing tool, our customers are generally not aware of its existence," Ghosemajumder said. "They were not able to see the attacks as being different from regular log-in activities, and also they had no idea there was a common tool available to enable the attack."

Ghosemajumder noted, however, that his company's Shape Botwall Service is able to detect and protect against Sentry MBA-based attacks. In addition, Shape Security has produced a detailed technical overview of some of the indicators that should alert any enterprise when being attacked by Sentry MBA. By default, Sentry MBA uses only five User Agent strings in the tool.

"If you decide to blacklist these User Agent strings, you should recognize that they can be changed to bypass such a control," Shape Security warns in its technical overview.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.