Automatically Detect Weak Passwords from Large Password Lists in Python

This Python script identifies weak passwords from a list by checking length, common patterns, sequential characters, and uniform characters, returning those that fail the security checks.

Easy Python 3.9+ Jun 28, 2026 Strings & text 2 views 0 copies

password security validation detection strings

Python code

30 lines

Python 3.9+

import re

COMMON_PASSWORDS_FILE = "common_passwords.txt"

def is_weak(password):
    # Check length
    if len(password) < 8:
        return True
    # Check for common patterns
    if password.lower() in {"password", "123456", "qwerty", "letmein", "admin", "welcome"}:
        return True
    # Check for sequential characters
    if re.search(r"(012|123|234|345|456|567|678|789|890)", password):
        return True
    # Check if all same character
    if len(set(password)) == 1:
        return True
    return False

def detect_weak_passwords(password_list):
    weak_passwords = []
    for pwd in password_list:
        if is_weak(pwd):
            weak_passwords.append(pwd)
    return weak_passwords

if __name__ == "__main__":
    sample_list = ["hello1", "password", "abcdefgh", "11111111", "strongPass1", "12345678", "qwerty123"]
    weak = detect_weak_passwords(sample_list)
    print(f"Weak passwords found: {weak}")

Output

stdout

Weak passwords found: ['password', '11111111', '12345678', 'qwerty123']

How it works

The is_weak function applies multiple rules: short passwords (under 8 characters) are flagged immediately. It checks against a set of common passwords (case-insensitive). Regular expressions detect sequential digits like '123' or '890'. Finally, passwords consisting entirely of the same character are considered weak. The detect_weak_passwords function iterates through the input list and collects all weak ones for reporting.

Common mistakes

Not normalizing case before comparing against common password lists, missing variations like 'Password'.
Using a small or static common password list instead of loading a comprehensive file like common_passwords.txt.
Forgetting to check for sequential patterns like 'abc' or keyboard walks (e.g., 'qwerty').
Applying the same rule set to all contexts without allowing customization (e.g., minimum length requirements may differ).

Variations

Use a dynamic list from a file by reading common_passwords.txt with open() and splitting lines.
Integrate with a library like zxcvbn for more sophisticated strength estimation based on entropy and patterns.

Real-world use cases

Auditing user-submitted passwords during account registration to enforce strength policies.
Scanning leaked password databases to quickly flag reused or weak credentials for forced reset.
Integrating into a CI/CD pipeline that checks configuration files for default or weak passwords.

Automatically Detect Weak Passwords from Large Password Lists in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Strings & text

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Strings & text

Keep learning

Tutorials

Quizzes