What is Overly Restrictive Account Lockout (CWE-645)?

TL;DR: Overly restrictive account lockout mechanisms can be exploited by attackers to deny service to legitimate users, disrupting availability. Fix this issue by implementing smarter throttling techniques.

What is Overly Restrictive Account Lockout Mechanism?

Overly Restrictive Account Lockout Mechanism (CWE-645) is a type of security misconfiguration vulnerability where account lockout mechanisms are too restrictive and can be easily triggered. As defined by the MITRE Corporation under CWE-645, and classified by the OWASP Foundation under general security misconfiguration guidelines…

Quick Summary

Overly Restrictive Account Lockout Mechanism allows attackers to perform denial-of-service attacks by causing legitimate users’ accounts to be locked out after minimal failed login attempts. This disrupts service availability and can lead to financial losses due to decreased user access.

Jump to: Quick Summary · Overly Restrictive Account Lockout Mechanism Overview · How Overly Restrictive Account Lockout Mechanism Works · Business Impact of Overly Restrictive Account Lockout Mechanism · Overly Restrictive Account Lockout Mechanism Attack Scenario · How to Detect Overly Restrictive Account Lockout Mechanism · How to Fix Overly Restrictive Account Lockout Mechanism · Framework-Specific Fixes for Overly Restrictive Account Lockout Mechanism · How to Ask AI to Check Your Code for Overly Restrictive Account Lockout Mechanism · Overly Restrictive Account Lockout Mechanism Best Practices Checklist · Overly Restrictive Account Lockout Mechanism FAQ · Vulnerabilities Related to Overly Restrictive Account Lockout Mechanism · References · Scan Your Own Site

Overly Restrictive Account Lockout Mechanism Overview

What

Overly restrictive account lockout mechanisms are too sensitive and can be triggered after a small number of incorrect login attempts.

Why it matters

This vulnerability allows attackers to perform denial-of-service attacks by causing legitimate users’ accounts to be locked out, disrupting service availability.

Where it occurs

It typically happens in web applications that implement overly simplistic account lockout mechanisms without considering IP addresses or increasing timeouts based on the number of failed login attempts.

Who is affected

Users and organizations relying on such restrictive lockout policies are at risk of being locked out during legitimate usage scenarios, leading to service disruptions.

Who is NOT affected

Applications implementing intelligent throttling mechanisms that take IP address into account and increase lockout timeouts as the number of incorrect login attempts increases are not vulnerable.

How Overly Restrictive Account Lockout Mechanism Works

Root Cause

The root cause lies in overly restrictive account lockout mechanisms that trigger too easily, causing legitimate users’ accounts to be locked out after minimal failed login attempts.

Attack Flow

1. The attacker identifies the lockout mechanism’s threshold.
2. They perform a series of incorrect login attempts from multiple IP addresses.
3. Legitimate user accounts are locked out due to the restrictive policy.
4. Service availability is disrupted for legitimate users.

Prerequisites to Exploit

• The application must have an overly restrictive account lockout mechanism in place.
• Attackers need access to perform multiple failed login attempts without being detected or blocked by other security measures.

Vulnerable Code

def attempt_login(username, password):
    if not authenticate_user(username, password):
        increment_failed_attempts(username)
        if get_failed_attempts(username) >= 3:
            lockout_account(username)

This code allows the account to be locked out after just three failed login attempts without considering IP addresses or increasing timeouts.

Secure Code

def attempt_login(username, password):
    if not authenticate_user(username, password):
        increment_failed_attempts(username)
        if get_ip_address() in suspicious_ips:
            lockout_account(username)
        elif get_failed_attempts(username) >= 10:
            increase_lockout_timeout(username)

This code takes IP addresses into account and increases the lockout timeout after multiple failed attempts.

Business Impact of Overly Restrictive Account Lockout Mechanism

Availability

• Legitimate users’ accounts are locked out, leading to service disruptions.
• Financial losses due to decreased user access and potential customer churn.

Integrity

• None directly impacted by this vulnerability.

Confidentiality

• None directly impacted by this vulnerability.

Overly Restrictive Account Lockout Mechanism Attack Scenario

1. The attacker identifies the lockout mechanism’s threshold through reconnaissance.
2. They perform a series of incorrect login attempts from multiple IP addresses to evade detection.
3. Legitimate user accounts are locked out due to the restrictive policy after minimal failed login attempts.
4. Service availability is disrupted for legitimate users, leading to customer complaints and potential financial losses.

How to Detect Overly Restrictive Account Lockout Mechanism

Manual Testing

• Simulate multiple failed logins from different IP addresses.
• Verify if the account gets locked out too quickly after a small number of incorrect attempts.

Automated Scanners (SAST/DAST)

Static analysis can detect overly restrictive lockout thresholds defined in code, while dynamic testing simulates login attempts to observe actual behavior.

PenScan Detection

PenScan’s automated scanners use ZAP and Wapiti to identify overly restrictive account lockout mechanisms by simulating multiple failed logins.

False Positive Guidance

False positives may occur if the mechanism is designed to be strict but includes IP-based throttling or increasing timeouts based on login attempts.

How to Fix Overly Restrictive Account Lockout Mechanism

• Implement more intelligent password throttling mechanisms that take IP address into account.
• Increase lockout timeouts as the number of incorrect login attempts increases.
• Consider alternatives such as presenting users with a puzzle to solve, making it harder for attackers to brute-force passwords.

Framework-Specific Fixes for Overly Restrictive Account Lockout Mechanism

Python/Django

def attempt_login(username, password):
    if not authenticate_user(username, password):
        increment_failed_attempts(username)
        if get_ip_address() in suspicious_ips:
            lockout_account(username)
        elif get_failed_attempts(username) >= 10:
            increase_lockout_timeout(username)

Java

public void attemptLogin(String username, String password) {
    if (!authenticateUser(username, password)) {
        incrementFailedAttempts(username);
        if (isSuspiciousIP(getIpAddress())) {
            lockoutAccount(username);
        } else if (getFailedAttempts(username) >= 10) {
            increaseLockoutTimeout(username);
        }
    }
}

Node.js

function attemptLogin(username, password) {
    if (!authenticateUser(username, password)) {
        incrementFailedAttempts(username);
        if (isSuspiciousIP(getIpAddress())) {
            lockoutAccount(username);
        } else if (getFailedAttempts(username) >= 10) {
            increaseLockoutTimeout(username);
        }
    }
}

PHP

function attemptLogin($username, $password) {
    if (!authenticateUser($username, $password)) {
        incrementFailedAttempts($username);
        if (isSuspiciousIP(getIpAddress())) {
            lockoutAccount($username);
        } else if ($failed_attempts >= 10) {
            increaseLockoutTimeout($username);
        }
    }
}

How to Ask AI to Check Your Code for Overly Restrictive Account Lockout Mechanism

Overly Restrictive Account Lockout Mechanism Best Practices Checklist

• ✅ Implement more intelligent password throttling mechanisms that take IP address into account.
• ✅ Increase lockout timeouts as the number of incorrect login attempts increases.
• ✅ Consider alternatives such as presenting users with a puzzle to solve, making it harder for attackers to brute-force passwords.
• ✅ Use rate-limiting techniques to prevent excessive failed login attempts from a single IP address.
• ✅ Monitor and analyze login patterns to detect suspicious activity before accounts are locked out.

Overly Restrictive Account Lockout Mechanism FAQ

How does an overly restrictive account lockout mechanism work?

An overly restrictive account lockout mechanism triggers too easily, locking out legitimate users after a small number of incorrect login attempts.

Why is it important to prevent overly restrictive account lockouts?

Preventing overly restrictive account lockouts ensures availability and prevents denial-of-service attacks that can disrupt normal user access.

Can you show me an example of vulnerable code for CWE-645?

Vulnerable code typically lacks intelligent mechanisms like IP-based throttling or increasing timeouts with more login attempts.

How do I detect overly restrictive account lockout vulnerabilities in my application?

Manual testing involves simulating multiple failed logins and observing if the account gets locked out too quickly. Automated scanners can also flag such patterns.

What are some best practices to fix CWE-645?

Implementing IP-based throttling or increasing lockout timeouts based on login attempts helps mitigate overly restrictive account lockouts.

How does OWASP categorize this vulnerability?

This vulnerability is not directly mapped to a specific OWASP category, but it aligns with general security misconfiguration guidelines.

What are some real-world consequences of an overly restrictive account lockout mechanism?

Users may be locked out of their accounts, leading to service disruptions and potential financial losses due to decreased user access.

Vulnerabilities Related to Overly Restrictive Account Lockout Mechanism

References

• MITRE - CWE-645
• NVD - NIST

Scan Your Own Site

Manual code review catches what you know to look for. An automated scan catches what you didn’t. Scan your own website using PenScan to find Overly Restrictive Account Lockout Mechanism and other risks before an attacker does.