CVE-2020-13357: 
GitLab vulnerability analysis and mitigation

An unauthorized access vulnerability was discovered in GitLab CE/EE versions >= 13.1 to <13.4.7, >= 13.5 to <13.5.5, and >= 13.6 to <13.6.2 that allowed unauthorized users to access user lists corresponding to feature flags in projects. The vulnerability was assigned CVE-2020-13357 and was reported through GitLab's HackerOne bug bounty program (GitLab Release, NVD).

The vulnerability is classified as an Authorization Bypass Through User-Controlled Key (CWE-639). It received a CVSS v3.1 Base Score of 4.3 (Medium) with the vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N, indicating network accessibility, low attack complexity, and low privileges required for exploitation (NVD).

The vulnerability allowed unauthorized users to access and enumerate feature flag user lists of any private or public project, potentially exposing sensitive user information and project configurations (GitLab Release).

The vulnerability could be exploited by manipulating the user_list_id parameter in feature flag-related requests, allowing attackers to enumerate and access feature flag user lists across different projects, including private ones (GitLab Issue).

The vulnerability was patched in GitLab versions 13.4.7, 13.5.5, and 13.6.2. Users running affected versions are strongly recommended to upgrade to the latest version of their respective release series (GitLab Release).