CVE-2022-2525 is a critical security vulnerability pertaining to the Improper Restriction of Excessive Authentication Attempts discovered in the GitHub repository, janeczku/calibre-web, prior to version .6.20. Calibre-web is a popular web app providing a clean interface for browsing, reading, and managing your e-book collection. This vulnerability allows attackers to perform a brute-force attack to gain unauthorized access to user accounts without being restricted by the number of authentication attempts. In this post, we will provide a detailed analysis of this vulnerability, including a code snippet, links to relevant references, and exploit details.

Code Snippet

The improper restriction of authentication attempts exists within the login function of CPS (calibre-web) due to inadequate handling of failed login attempts. Below is the code snippet with the vulnerability in the 'cps/' file:

@app.route('/login', methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('index'))

    form = LoginForm(request.form)
    if request.method == 'POST' and form.validate():
        user = ub.session.query(ub.User).filter(ub.User.nickname ==
        if user and check_password_hash(user.password,
            flash(gettext('Welcome, %(username)s!', username=user.nickname), category="success")
            return redirect(request.args.get('next') or url_for('index'))
        flash(gettext('Invalid username or password'), category="error")

    return render_template('login.html', title='Sign In', form=form)

In the above code snippet, no limit is placed on the count of failed login attempts, enabling potential brute-force attacks.

Original References

1. CVE-2022-2525 Vulnerability Disclosure in NVD
2. GitHub Repository janeczku/calibre-web
3. Calibre-web Changelog with Security Fixes

Exploit Details

An attacker can exploit the CVE-2022-2525 vulnerability to perform a brute-force attack on user accounts in calibre-web prior to version .6.20. The attacker submits a series of login attempts using different password combinations, eventually finding the correct password without being limited or restricted by the system.


The calibre-web project recognized this vulnerability and released a patch in version .6.20 to address the issue. The fix involves implementing a limit on the number of excessive authentication attempts and introducing a time delay mechanism for preventing brute-force attacks. By upgrading to calibre-web version .6.20 or later, you can protect your e-book collection from unauthorized access due to this vulnerability. To upgrade your calibre-web instance, refer to the official documentation.


CVE-2022-2525 is a critical security vulnerability that poses a threat to users of calibre-web prior to version .6.20. By understanding the vulnerability, identifying the vulnerable code, and implementing the appropriate measures, users can secure their e-book collections and prevent unauthorized access by potential attackers.


Published on: 04/15/2023 13:15:00 UTC
Last modified on: 04/24/2023 18:50:00 UTC