How do credential stuffing attacks exploit enumeration flaws

Question

Enumeration flaws reveal valid usernames or account details. How do attackers use this information to automate credential stuffing attacks?

Answer 1

​Credential stuffing attacks exploit enumeration flaws by identifying valid usernames or account identifiers through application responses. Once attackers confirm which usernames exist, they automate login attempts using stolen credentials, increasing the likelihood of unauthorized access.​

How Enumeration Flaws Facilitate Credential Stuffing?

1. User Enumeration: Applications that provide distinct responses for valid and invalid usernames (e.g., "User not found" vs. "Incorrect password") inadvertently allow attackers to verify the existence of specific accounts.​

2. Credential Verification: With a list of valid usernames, attackers use automated tools to test stolen password combinations, often obtained from previous data breaches. This process, known as credential stuffing, leverages the common practice of password reuse across multiple platforms.​

3. Automation Tools: Attackers employ tools like Sentry MBA, Snipr, or OpenBullet to automate login attempts, manage IP rotation, and bypass security measures such as CAPTCHAs. These tools can distribute login attempts across various IP addresses, making detection more challenging.​

Real-World Example

An attacker targets a website's login page that reveals whether a username exists. By inputting a list of usernames and analyzing the responses, the attacker compiles a list of valid accounts. Using credential stuffing tools, they then attempt to log in with commonly used passwords or credentials from previous breaches, successfully accessing accounts where users have reused passwords.​

Mitigation Strategies

To protect against such attacks:

• Implement Generic Error Messages: Avoid revealing whether a username or password is incorrect.​

• Rate Limiting and Account Lockout Policies: Limit the number of login attempts from a single IP address or account.​

• Multi-Factor Authentication (MFA): Add an extra layer of security beyond just usernames and passwords.​

• Monitor for Unusual Activity: Use analytics to detect and respond to abnormal login patterns.​

By addressing enumeration flaws and implementing robust security measures, organizations can significantly reduce the risk of credential stuffing attacks.