CVE-2021-29621: 
Python vulnerability analysis and mitigation

CVE-2021-29621 affects Flask-AppBuilder, a development framework built on top of Flask, versions 3.2.3 and earlier. The vulnerability was discovered and disclosed in May 2021, allowing unauthenticated users to perform user enumeration through database authentication by timing the server's response during login attempts (GitHub Advisory).

The vulnerability is classified as an Observable Response Discrepancy (CWE-203) with a CVSS v3.1 Base Score of 5.3 (Medium). The attack vector is network-based (AV:N) with low attack complexity (AC:L), requiring no privileges (PR:N) or user interaction (UI:N). The scope is unchanged (S:U) with low confidentiality impact (C:L) and no impact on integrity (I:N) or availability (A:N) (NVD).

The vulnerability allows malicious actors to enumerate existing user accounts in the system by measuring the response time differences during login attempts. This information disclosure could be used as a stepping stone for further attacks, such as brute force attempts or targeted phishing campaigns (GitHub Advisory).

Users are advised to upgrade to Flask-AppBuilder version 3.3.0 or higher, which contains the fix for this vulnerability. The fix was implemented through a patch that balances the response time for authentication attempts (GitHub Patch).