CVE-2023-5831: 
GitLab vulnerability analysis and mitigation

CVE-2023-5831 affects GitLab CE/EE versions starting from 16.0 before 16.3.6, all versions starting from 16.4 before 16.4.2, and all versions starting from 16.5.0 before 16.5.1 which have the supersidebarlogged_out feature flag enabled. The vulnerability was internally discovered by GitLab on October 20, 2023, at 11:03 UTC, where a change in the GitLab sidebar feature resulted in unintentional disclosure of GitLab version metadata to unauthorized actors (GitLab Security Release).

The vulnerability occurs when the supersidebarlogged_out feature flag is enabled, causing self-managed GitLab instances to send version-checks to version.gitlab.com each time a page is opened on their GitLab instance. This results in the hostnames and current versions of self-managed GitLab instances being sent to version.gitlab.com for any user accessing any page, regardless of whether version-check was enabled. The vulnerability has been assigned a CVSS v3.1 base score of 3.7 (Low) with the vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N (NVD).

The vulnerability leads to the unintentional disclosure of GitLab version metadata to unauthorized actors. The collected information was only accessible to some GitLab team members and was not exposed externally. GitLab has confirmed they are working to purge the erroneously collected data from their database (GitLab Security Release).

GitLab has released patches in versions 16.5.1, 16.4.2, and 16.3.6. It is strongly recommended that all installations running affected versions be upgraded to the latest version as soon as possible. The vulnerability is already patched in GitLab.com (GitLab Security Release).