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In a world where cyberattacks are becoming more frequent and sophisticated, credential stuffing has emerged as a critical threat to organizations. One of the most significant vulnerabilities businesses face today is the widespread practice of credential reuse. Despite constant warnings to avoid using the same passwords across multiple accounts, many users continue to recycle their usernames and passwords for convenience.
This risky habit creates a fertile ground for credential stuffing attacks, where cybercriminals leverage stolen, reused credentials to gain unauthorized access to systems. Understanding the dangers of credential stuffing and implementing robust security measures is crucial to protecting sensitive data. This article explores how credential stuffing works and how you can strengthen your defenses against this growing threat.
Main points:
Credential stuffing targets reused passwords: Attackers use stolen credentials to access many accounts. Users increase the risk by reusing passwords across sites.
Multi-factor authentication (MFA) adds a barrier by requiring an extra step to access accounts, blocking attackers even if they have the right credentials.
Passwordless login methods eliminate the need for passwords, preventing attackers from exploiting stolen credentials.
What is credential stuffing?
Credential stuffing is a type of cyberattack where adversaries use previously breached credentials to gain unauthorized access to accounts across various services. These attacks are based on the premise that people reuse usernames and passwords across online accounts.
In a credential stuffing attack, cybercriminals use automated bots to systematically attempt logins with the stolen credentials on a wide range of websites. These automated attempts are made en masse, targeting many accounts across numerous sites in the hope that some login attempts will succeed.
Credential stuffing is a growing concern for organizations of all sizes, and its scale is staggering. According to the Verizon Data Breach Investigations Report (DBIR), 88% of attacks against basic web applications involved the use of stolen credentials. This shows just how prolific these attacks have become and underscores the widespread nature of the threat.
Credential stuffing attacks are also becoming increasingly sophisticated. According to Descope's 2025 State of Customer Identity report, 87% of organizations still rely on username/password authentication, yet only 2% believe passwords effectively balance security and user experience — a reliance gap that keeps credential stuffing viable. As more personal data gets exposed in breaches, the number of credential stuffing attempts continues to rise, with cybercriminals now targeting not just user accounts but also high-value systems, such as corporate networks and cloud services.
Credential stuffing vs. brute force attacks
Credential stuffing is a subset of brute force attacks. While both these attacks follow some common themes, they have several noteworthy differences.
While credential stuffing attacks use stolen passwords to attempt logins, brute force attacks try to guess passwords using dictionaries of common phrases or popular “boilerplate” passwords like Qwerty, 123abc, and Password.
How bots are programmed in credential stuffing and brute force attacks also differ. While credential stuffing bots are programmed to try the same username-password combination across various sites, brute force bots are programmed to try multiple username-password combinations on the same site.
Credential stuffing and brute force attacks share one key similarity. They both exploit passwords' inherent weaknesses. Passwords are a flawed authentication method. Brute force attacks assume people use common phrases as passwords. Credential stuffing relies on the assumption that people reuse passwords across accounts.
Trait | Credential Stuffing | Brute Force Attacks |
|---|---|---|
Attack Method | Retrying compromised passwords | Attempting to guess passwords |
Credential Source | Data breaches, the Dark Web, malware | Common phrases, popular passwords, or (rare) simply random combinations |
Bot Behavior | Trying the same username and password across various sites | Trying multiple usernames and passwords on the same site |
Detection Signal | Harder to detect; each attempt uses a valid-looking credential pair, often against a different account | Easier to detect; generates repeated failed attempts against the same account |
Credential stuffing vs. credential harvesting
Then, there’s credential harvesting vs. credential stuffing. While both tactics involve compromising user accounts, they represent different stages in the cybercrime cycle. Credential stuffing leverages existing compromised data for unauthorized access across multiple platforms, whereas credential harvesting focuses on the initial acquisition of user credentials through deceitful means.
As the name suggests, credential harvesting aims to collect username and password combinations directly from users through deception. This technique often involves phishing, such as sending emails that appear to be from reputable sources asking for sensitive information, creating fake websites that mimic legitimate ones to trick users into entering their login details or distributing malware that captures keystrokes.
Credential harvesting aims to amass as many valid credentials as possible, which can later be used in credential stuffing attacks, sold on the dark web, or leveraged to gain direct unauthorized access to systems and data.
How credential stuffing works
Here’s how a typical credential stuffing attack looks in practice:
Attackers get hold of stolen usernames and passwords. This is a trivial exercise. Billions of leaked passwords are on the dark web. Phishing attacks are still successful.
Attackers feed the stolen username-password pairs into a botnet, a network of Internet-connected devices controlled by the attacker. Bot attacks and automation magnify the scale and impact of credential stuffing.
The botnets simultaneously try to “stuff” stolen credentials into many website login forms. Botnets often distribute attempts across thousands of legitimate-looking residential IPs (held by compromised devices) to stay below per-IP detection thresholds.
If a login is successful, attackers usually steal personal data, including credit card details and other information, for profit or to carry out further attacks.
A successful credential stuffing attack presents many downstream opportunities for the attacker.
They can sell the validated, stolen login credentials online. Streaming and entertainment services are common victims.
They can commit ecommerce fraud by using saved payment details to complete high-value transactions for personal use or resale.
They can change the password and other settings to lock the user out of their account and steal their online identity.
If the account takeover is successful, the attacker can use the victim’s account as a vector to carry out new scams. For example, a Facebook scam involved attackers. They asked for money by pretending to be the victim's friend, stranded in another country.
If the attacker breaks into a victim’s work account, they can access sensitive information. They can sell it to the highest bidder or use it to ransom the company. Because people often reuse passwords across personal and work accounts, a single breach can expose both.
Learn more: Broken Authentication 101
Why is credential stuffing on the rise?
Credential stuffing is not new, but it has grown in popularity in recent years. Research shows that one in five login attempts comes from bots, which attackers use in credential stuffing attacks. Various market, technological, and societal factors contribute to credential stuffing attacks’ popularity:
Passwords are fallible: Users often reuse them across accounts, even though they know it’s risky. Email addresses often double as usernames, increasing the likelihood that stolen credentials will be used across many websites.
It's scalable and hard to detect. Botnets obfuscate their IP address to bypass security blocklists. Bots are programmed to attempt login on a web application only once, bypassing lockouts caused by repeated failed login attempts.
It's low-cost. It's easy to get credentials and launch credential stuffing attacks. Leaked passwords and stuffing tools are widespread. Attackers only need a few hundred dollars and some patience to strike digital gold.
More digital identities are online: Almost every aspect of life is now online, and there’s an app for everything. Remote work, social media, and digitalization have changed our lives. This leads to an increase in online accounts and access credentials, which in turn increases the attack surface for credential stuffing.
Credential stuffing risks and impact
Credential stuffing raises various concerns for businesses. It affects their operations, legal status, finances, and reputation. Let’s explore some of the risks and outcomes of these attacks:
Data breaches: Credential stuffing can allow unauthorized access, leading to data breaches. These breaches expose sensitive data, endanger user privacy, and put companies at risk of legal trouble. Under data protection laws such as GDPR and CCPA, organizations can be fined or sued for data breaches.
Account takeover (ATO): Attackers can hijack user accounts. This is especially harmful for accounts with special access, as it leaves critical system areas vulnerable. ATOs can tarnish a brand’s reputation, deterring customer engagement and eventually impacting the bottom line.
System downtime: A high volume of login attempts can slow or crash the system, affecting user experience and disrupting operations. Over time, repeated disruptions can lead to customer turnover and lost revenue.
How to prevent credential stuffing
Theoretically, complete credential stuffing prevention is possible. People can achieve this by using unique passwords for each account. But the average person has 100 passwords to remember. This makes password reuse the most convenient, though unsafe, option.
Password managers are another option. One in five Americans uses them. However, attackers need just one set of stolen credentials to bypass their security. There’s also the fear of forgetting the master password or it being stolen. Attackers could then access all the victims’ login data.
Organizations can take measures to stop attackers. These measures prevent attackers from using stolen credentials and ensure that they cannot impersonate users.
Passwordless authentication
Passwordless authentication can stop credential stuffing at the source. If there are no passwords to steal, attackers will move on to their next target. Passwordless authentication verifies users with something they have or are. It uses a device, a security key, or biometrics, not a password. Examples of passwordless auth methods include:
One-time passwords (OTPs): These dynamically generated codes are emailed or texted to users before a set expiration.
Magic links: These clickable links feature embedded tokens. They’re delivered to the user via SMS or email.
Passkeys: A passkey is a FIDO2 credential based on a public-private key pair. The private key is stored securely on the user's device, and the public key is registered with the service. Users unlock the passkey with biometrics or a device PIN to complete authentication.
Passwordless authentication improves users' login experiences and reduces organizations' overhead from password storage, management, and resets.
Multi-factor authentication
For organizations that need more time to be ready to ditch passwords, multi-factor authentication (MFA) helps stop credential stuffing attacks. MFA adds an extra factor after the username-password combination is entered. This can be a one-time password or a fingerprint authentication. The attacker will not have access to any of these.
An even more effective variant is phishing-resistant MFA. This approach leverages strong authentication factors that are harder to replicate, such as hardware tokens and certificate-based authentication.
MFA prevents the attacker from accessing the user’s account, but it does not prevent the attacker from knowing that the username and password are valid.
Password hashing
Organizations can use password hashing before storing passwords in their databases, turning the password into a scrambled representation. This won’t stop password theft or decryption, but it will give users more time. They can change their passwords on other accounts after a credential theft.
Bot protection/reCAPTCHA
ReCAPTCHAs show puzzles or challenges. They're easy for humans but hard for bots. Integrating reCAPTCHA can stop bots from submitting login requests, making it harder for attackers to run credential stuffing attacks.
Breached password monitoring
Organizations can check entered credentials against compromised databases like Have I Been Pwned. This helps identify and stop credential stuffing. In fact, organizations can inform the user if the login details match the breached credentials, ask the user to change their password, and request extra factors through step-up authentication.
Rate limiting
While some security measures safeguard credentials to stop credential stuffing upstream, others exist to halt attackers in their tracks. Rate limiting and anomaly detection are two connected strategies that reduce the risk of brute-force attacks.
Rate limiting throttles the number of logins that a client can attempt within a particular timeframe. Humans, unlike bots, don’t attempt dozens of logins in a matter of seconds, so rate limiting can protect against unusual activity.
Prevent credential stuffing with Descope
Protecting applications from the widespread risk of credential stuffing is essential. Developers and product owners must take critical actions, including setting up in-house protection systems.
Descope prevents and mitigates credential stuffing threats with MFA, bot protection, rate limiting, and a rich connector ecosystem (including Google reCAPTCHA, Fingerprint, Arkose Labs, and Forter) for third-party anomaly detection. Our drag-and-drop customer authentication platform helps organizations easily add signup and login capabilities.
Sign up for a Free Forever account with Descope to start your journey towards credential stuffing prevention. Have questions about our platform? Book time with our auth experts.
