At a time when new data leaks are making headlines almost daily, IT security teams - especially in critical organizations, the manufacturing industry and healthcare - are under enormous pressure. It is no longer enough to simply harden your own infrastructure; the biggest vulnerability often lies outside of your control: in the careless handling of passwords by users.
Today we look at a particularly insidious threat that exploits this very problem and can cause enormous damage: the credential stuffing attack.
A. What is credential stuffing?
Credential stuffing is a type of cyberattack in which stolen combinations of usernames and passwords are tested en masse and automatically against the login forms of various web services.
The attack is based on the assumption that many users use the same login data for several different accounts. The attackers use login data that they have previously captured in data breaches from websites that are often less protected.
Analogy for beginners:
Imagine a thief captures a bunch of keys from a small, insecure shed (the insecure data breach). Now, instead of picking the lock on the shed, the thief runs with it to the locks of banks, offices and homes (the well-protected web services) in the hope that the occupants have used the same key for convenience.
B. What makes credential stuffing so effective?
The effectiveness of credential stuffing relies on four critical factors that make the attack one of the biggest threats to modern organizations:
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Human behavior (password reuse): This is the Achilles heel of digital security. Study after study shows that a significant percentage of users use identical or very similar passwords for a variety of accounts - from online stores to critical enterprise applications.
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Availability of login credentials: The sheer volume of leaked data sets on the darknet, often in the form of so-called "combo lists", is gigantic. This pool grows after every major data leak.
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Automation: The attacks are not carried out manually. Special bots and scripts can launch thousands of login attempts per minute against a large number of targets without the attackers having to be physically present.
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Stealth (low-and-slow attacks): Unlike fast, obvious attacks, credential stuffing campaigns can be configured to make only a low number of attempts per IP address and time window. This makes detection by conventional rate-limiting measures (limiting login attempts) more difficult.
Especially in areas such as healthcare (sensitive patient data), the manufacturing industry (intellectual property, production control) and critical organizations (infrastructure), a successful credential stuffing attack poses a huge risk to business continuity and data security.
C. Credential stuffing vs. brute force attacks: The differences
Although both types of attack have the goal of gaining access to an account, they differ fundamentally in their method and starting point:
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Feature
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Credential stuffing
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Brute force attack
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Starting point
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Valid credentials from another data leak.
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No known credentials.
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Target of the attack
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Exploitation of password reuse.
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Guessing the unknown password by systematically trying all possible character combinations.
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Speed/efficiency
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High success rate as the passwords are already correct.
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Very slow and inefficient (except for extremely weak passwords).
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Perception by IT
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Often looks like legitimate login attempts by real users, makes recognition more difficult.
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Clearly recognizable by a very high number of failed attempts against a single account.
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In short, a brute force attack is an attempt to guess an unknown password; credential stuffing is an attempt to reuse a known password that has been stolen elsewhere.
D. How can credential stuffing be prevented?
Preventing credential stuffing attacks requires a combination of technical controls, organizational measures and user awareness.
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Technical controls
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Implementation of MFA (multi-factor authentication): The most effective single measure. Even if attackers have the correct combination of username and password, they will fail at the second factor (e.g. a time-based one-time password or biometric confirmation). This should be made mandatory wherever possible.
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Advanced bot detection and rate limiting: Use WAFs (Web Application Firewalls) and specialized bot management solutions to detect and block unusual login patterns, targeted IP address rotation and the typical behavior of credential stuffing bots.
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Monitor and blacklist known leaks: Monitor publicly available or subscription-based lists of compromised credentials. Warn or block accounts whose passwords have been exposed in a recent data leak.
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Abolish the password: Use future-proof methods such as passwordless authentication (e.g. FIDO2/WebAuthn standards). These use cryptography to validate credentials, eliminating secret passwords that could be stolen and reused.
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Organizational and user measures
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Password policies: Enforce the use of long and complex passwords. More importantly, prohibit the reuse of passwords by indicating the use of password managers in your policies or by making them available.
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Training: Train employees and users regularly on the dangers of password reuse and the importance of MFA.
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Error checking: Make sure that error messages at login do not reveal whether the user name exists or whether the password is incorrect. A generic message ("Login failed.") makes it difficult to scan for valid usernames.
Credential stuffing is a direct attack on human convenience and a direct result of increasingly frequent data leaks. It exploits a fundamental weakness - password reuse - to damage organizations in sectors such as healthcare, manufacturing and critical infrastructure. The attack vector is particularly dangerous as successful accesses often look like legitimate logins and the damage - from intellectual property theft to compromising patient data - can be devastating.
For IT specialists, it is clear that the mere complexity of passwords is no longer enough. Defense requires a two-pronged strategy:
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The widespread and mandatory introduction of MFA is the most important immediate measure to neutralize this type of attack.
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In the long term, we must move away from dependence on static passwords. Implementing passwordless authentication solutions (such as FIDO2) is the most effective way to eliminate the credential stuffing attack surface for good.
By investing in advanced bot management, consistent user education and modern authentication methods, you will significantly increase your organization's digital resilience and secure your critical data and processes.
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