CVE-2022-21659 is a user enumeration vulnerability identified in Flask-AppBuilder, an application development framework built on top of the Flask web framework. This vulnerability allows an unauthenticated attacker to determine valid usernames by measuring differences in server response times during login attempts. Specifically, the timing discrepancy occurs because the application processes login requests differently depending on whether the username exists, enabling an attacker to infer valid accounts without needing credentials or authentication. This type of vulnerability falls under CWE-203 (Information Exposure Through Discrepancy). The vulnerability does not impact the confidentiality, integrity, or availability of the system directly but leaks sensitive information about user existence. The CVSS v3.1 base score is 5.3 (medium severity) with vector AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N, indicating that the attack can be performed remotely without privileges or user interaction and results in limited confidentiality impact. There are no known workarounds, and users are advised to upgrade to Flask-AppBuilder version 3.4.4 or later to remediate the issue. No known exploits have been reported in the wild as of the publication date.

For European organizations using Flask-AppBuilder in their web applications, this vulnerability poses a moderate risk primarily related to information disclosure. By enumerating valid usernames, attackers can facilitate targeted attacks such as credential stuffing, phishing, or brute force attacks against identified accounts. This can lead to unauthorized access if weak or reused passwords are present. Although the vulnerability itself does not allow direct compromise, the leaked user information can be leveraged in multi-stage attacks. Organizations handling sensitive user data, especially in sectors like finance, healthcare, or government, could face increased risk of account compromise and subsequent data breaches. Additionally, the exposure of user existence information may violate privacy regulations such as the GDPR if personal data is involved, potentially leading to compliance issues and reputational damage.

To mitigate this vulnerability, European organizations should promptly upgrade Flask-AppBuilder to version 3.4.4 or later, where the timing discrepancy issue has been addressed. Beyond upgrading, developers should implement consistent response times for login attempts regardless of username validity to prevent timing-based user enumeration. Employing account lockout or throttling mechanisms after multiple failed login attempts can reduce the feasibility of enumeration and brute force attacks. Additionally, implementing multi-factor authentication (MFA) can mitigate the risk of account compromise even if usernames are enumerated. Logging and monitoring login attempts for anomalous patterns can help detect enumeration activities early. Finally, organizations should review their privacy policies and ensure compliance with GDPR and other relevant regulations concerning user data exposure.