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Credential Stuffing

A credential stuffing attack is one of the most common and dangerous threats on the internet today. Attackers use stolen login credentials from data breaches and test them automatically across many websites. Because many users reuse the same passwords and usernames across services, attackers can often take over multiple accounts with a single dataset. This article explains how credential stuffing works, which industries are most affected, and which credential stuffing prevention measures actually work.

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At a
Glance

  1. 1. What Is a Credential Stuffing Attack?
  2. 2. How Does a Credential Stuffing Attack Work?
  3. 3. Why Do Attackers Use Bots for Credential Stuffing?
  4. 4. How Is Credential Stuffing Different from Brute Force and Password Spraying?
  5. 5. Which Industries and Companies Are Most at Risk?
  6. 6. What Are the Consequences of Credential Stuffing for Businesses?
  7. 7. What Is the Best Way to Stop Credential Stuffing Attacks?
  8. 8. Credential Stuffing Requires a Layered Defense
01

What Is a Credential Stuffing Attack?

A credential stuffing attack is the automated injection of stolen username-password pairs ("credentials") into website login forms to gain unauthorized access to user accounts.

Key characteristics at a glance:

  • Automated: Bots test millions of login combinations in a very short time.

  • Based on real data: The credentials come from hacks, phishing, or dark web marketplaces.

  • Large-scale: A single dataset is used against many services.

  • Hard to detect: The requests look like normal logins from legitimate users.

Statistics show that around 0.1% of leaked credentials actually result in a successful login on another service. Given lists containing millions of records, this is highly profitable for attackers — and why credential stuffing mitigation has become a top priority for security teams.

Sequence of an attack by means of credential stuffing
02

How Does a Credential Stuffing Attack Work?

A typical credential stuffing attack follows a clear pattern:

  1. Data acquisition: Attackers obtain login data from data breaches, phishing campaigns, or buy them on the dark web. Collections such as "Collection #1–5" have already exposed 2,2 billion username-password combinations in plain text.

  2. Bot setup: Attackers configure a bot that logs into multiple user accounts in parallel while spoofing different IP addresses.

  3. Attack execution: The bots test the credentials against login forms of many services simultaneously.

  4. Evaluation: Successful logins are flagged as "valid" and collected.

  5. Monetization: Attackers make unauthorized purchases, transfer funds, steal personal data, or sell the compromised accounts (e.g., streaming services) on black markets.

Code on a screen
03

Why Do Attackers Use Bots for Credential Stuffing?

Bots are essential for any credential stuffing attack because they combine speed with stealth. This is why effective credential stuffing prevention requires intelligent bot management.

  • Scalability: Millions of logins are possible within just a few hours.

  • Stealth through IP rotation: Modern credential stuffing software bypasses defenses by launching multiple login attempts that appear to come from different device types and IP addresses.

  • Low visibility: Malicious bots make login attempts indistinguishable from normal traffic — often the only indicator of an attack is a spike in overall login volume.

  • CAPTCHA bypass: Some tools circumvent CAPTCHA systems, spoof or obfuscate IP addresses, and adapt to common defense mechanisms.

White robot with glowing eyes: visual representing intelligent bot management by Myra Security
04

How Is Credential Stuffing Different from Brute Force and Password Spraying?

These three attack types are often confused, but they work very differently. The key difference: Brute force attacks guess credentials without context and usually fail against modern web applications with basic protections. A credential stuffing attack, however, can succeed – because even strong passwords don't help if users reuse them across services.

Feature
Credential Stuffing
Brute Force
Password Spraying

Basis

Real leaked credentials

Randomly generated passwords

List of common passwords

Target accounts

Many accounts in parallel

One or few accounts

Many accounts

Detectability

Hard to detect

Easy to detect

Medium

Success rate

Relatively high

Low against strong passwords

Medium

Prerequisite

Password reuse

Weak passwords

Common default passwords

Basis

Real leaked credentials

Target accounts

Many accounts in parallel

Detectability

Hard to detect

Success rate

Relatively high

Prerequisite

Password reuse

05

Which Industries and Companies Are Most at Risk?

Any service with a login function is a potential target. The most attractive targets include:

  • Banks and financial services – high transaction volumes, direct monetary value

  • Payment providers – immediate monetization possible

  • Public Sector and Healthcare – highly sensitive data vulnerable to fraud and extortion

  • Travel and tourism – valuable loyalty points and customer data

  • Online stores and e-commerce – stored payment details

  • Streaming services – accounts resold on the dark web

  • Corporate accounts – access to sensitive business data

The most likely targets are popular websites with strong brand recognition whose user credentials are available in dark web data dumps.

Password lettering
06

What Are the Consequences of Credential Stuffing for Businesses?

The impact of a successful attack is far-reaching:

  • Financial losses: Chargebacks, fraud damages, compensation payments

  • Reputational damage: Lasting loss of customer trust

  • Regulatory fines: GDPR penalties following data breaches

  • Operational burden: Support costs, account recovery, forensics

  • Long-term consequences: Leaked data is used for follow-up attacks years later

Computer screens with code
07

What Is the Best Way to Stop Credential Stuffing Attacks?

The best way to stop credential stuffing attacks is a layered defense combining technical and organizational controls. No single measure is enough – but the following building blocks work together to deliver reliable credential stuffing mitigation.

  • Multi-Factor Authentication (MFA): Multi-factor authentication is by far the strongest defense against most password-based attacks — a Microsoft analysis suggests MFA would have prevented 99.9% of account compromises.

  • Bot Management: Since these attacks are almost always automated, real-time bot management technology is often the best defense. Modern systems use behavioral analysis, machine learning, and device fingerprinting.

  • CAPTCHA and Adaptive Challenges: Adaptive CAPTCHAs – triggered only under suspicious conditions such as unusual login locations or rapid login attempts – improve security without hurting the user experience.

  • Device Fingerprinting: JavaScript can be used to collect information about user devices and create a unique "fingerprint" for each session, based on parameters such as operating system, language, browser, time zone, and user agent.

  • IP and Traffic Analysis: Correlating authentication traffic with proxy and IP intelligence, as well as known hosting provider IP ranges, helps identify highly distributed credential stuffing attacks.

  • Enforce password security: When assigning passwords, implement automated checks against known leaked passwords (e.g., HaveIBeenPwned), establish strong password policies, and encourage the use of password managers and passkeys.

  • Web Application Firewall: A modern WAF detects suspicious patterns in authentication traffic and blocks automated access attempts before they reach the login screen. 

08

Conclusion: Credential Stuffing Requires a Layered Defense

Credential stuffing is not a niche issue — it's a daily threat for every business with a login function. Individual measures like strong passwords or simple CAPTCHAs are no longer enough. The best way to stop credential stuffing attacks is to combine multi-factor authentication, intelligent bot management, adaptive challenges, and professional traffic monitoring into a coherent defense strategy.

FAQ on Credential Stuffing

In a credential stuffing attack, both username and password are already known — attackers simply test where they still work. In credential cracking, only the username is known, and the password is guessed using dictionaries or brute force.

About the author

Stefan Bordel

Senior Editor

About the author

Stefan Bordel has been working as Editor and Technical Writer at Myra Security since 2020. He is responsible for the strategic development and editorial management of all content formats – from website content and specialist publications to whitepapers, social media communication, and technical documentation. In this role, he combines solid expertise from IT journalism with in-depth technical understanding in the field of cybersecurity. As a long-time Linux enthusiast, he closely follows developments in the IT industry both professionally and personally.