In this post, we are going to discuss a vulnerability identified as CVE-2023-2106 found in the GitHub repository janeczku/calibre-web before version .6.20. The program calibre-web is a web app providing a clean interface for browsing, reading, and downloading eBooks using an existing Calibre database. Unfortunately, due to weak password requirements, the program suffered from a potential security issue. This post will provide an overview of the vulnerability, an example code snippet, links to original references, and exploit details. Stay with us!

CVE-2023-2106: The Vulnerability

The vulnerability CVE-2023-2106 is related to weak password requirements. Web applications implementing authentication mechanisms without robust password policies are susceptible to brute-force and dictionary attacks by allowing the usage of weak, easy-to-guess passwords. As a result, attackers could compromise user accounts and gain unauthorized access to sensitive information or perform malicious actions on behalf of the user.

In the case of the janeczku/calibre-web repository, prior to version .6.20, the program let users create accounts with weak passwords. It did not enforce rules such as minimum length, complexity (use of upper/lowercase letters, numbers, and special characters), or checking against commonly used passwords. Consequently, this made it vulnerable to attacks.

Code Snippet

To understand the vulnerability, let's examine a code snippet from the affected version of Calibre-web. In the below code, you can observe how the password for a new user is processed without any substantial checks or policies in place:

def create_new_user(username, password, email):
    new_user = User()
    new_user.nickname = username
    new_user.password = generate_password_hash(password)  # No strength validation = email
    new_user.role = ROLE_USER
    return new_user

In the code above, the create_new_user function takes a given username, password, and email as input and creates a new User object. Although the password is hashed using generate_password_hash(), there is no validation on its strength before storing it.

To mitigate this vulnerability, password policies must be enforced. For instance, a new function called is_password_strong could be added to verify the password strength before creating the user:

def is_password_strong(password):
    # Implement password strength checks here

def create_new_user(username, password, email):
    if not is_password_strong(password):
        raise ValueError("Weak password")
    new_user = User()
    # ... Rest of the code

Original References

The vulnerability was officially disclosed, and you can find the complete information in the links provided below:

1. CVE-2023-2106 entry at NIST National Vulnerability Database
2. GitHub repository janeczku/calibre-web
3. GitHub issue that addressed the vulnerability
4. GitHub Pull Request that fixed the issue in .6.20

Exploit Details

An attacker could perform a brute-force or dictionary attack by trying multiple password combinations against the targeted account. The success rate increases significantly given the lack of adequate password requirements.

To exploit this vulnerability, an attacker may use various brute-force tools or create a custom script that repeatedly sends login requests with various weak passwords until a correct one is identified.

There has been no reported incident related to this vulnerability, but it is important to upgrade janeczku/calibre-web to version .6.20 or later to prevent such attacks.


CVE-2023-2106 was a vulnerability caused by weak password requirements in janeczku/calibre-web. We discussed the vulnerability, provided a code snippet, original reference links, and exploit details. It is crucial to implement strong password policies in web applications to avoid falling victim to such attacks. Always make sure you are using the latest and most secure version of any software you are running, and stay safe!


Published on: 04/15/2023 14:15:00 UTC
Last modified on: 04/25/2023 16:29:00 UTC