The vulnerability CVE-2024-56433 affects shadow-utils (shadow) versions 4.4 through 4.17.0, specifically involving the initialization of the /etc/subuid file with an insecure default UID range (commonly 100000 through 165535 for the first user account). This default range can overlap with user IDs assigned within locally administered networks, creating a conflict that attackers can exploit. The exploitation vector involves leveraging the newuidmap utility, which is used to map user IDs for user namespaces, to gain unauthorized access to resources such as NFS-mounted home directories or same-host resources accessed via remote logins. This can lead to account takeover scenarios where an attacker with low privileges on the system can escalate access by exploiting the UID range overlap. The root cause is the insecure default initialization of the subuid resource, categorized under CWE-1188. The vulnerability requires local access and has a high attack complexity, with no user interaction required. The CVSS 3.1 score is 3.6, indicating low severity, primarily due to the limited scope and complexity of exploitation. No public exploits or active exploitation in the wild have been reported. The issue highlights the importance of system administrators avoiding UID conflicts by customizing /etc/subuid ranges to ensure they do not overlap with locally assigned UIDs on networks. Proper UID management and network segmentation can mitigate the risk. This vulnerability is relevant to Linux environments using shadow-utils, particularly those employing user namespaces and networked home directories.

The potential impact of CVE-2024-56433 is primarily unauthorized access and possible account takeover within affected Linux environments. If exploited, an attacker with low privileges could leverage UID range conflicts to access NFS home directories or other resources mapped via user namespaces, potentially compromising confidentiality and integrity of user data. However, the impact is limited by the requirement for local access and the high complexity of exploitation. Availability is not affected. Organizations with networked Linux systems using shadow-utils and user namespaces are at risk, especially where UID assignments are not carefully managed. This could lead to lateral movement within networks or unauthorized data access, impacting sensitive environments such as enterprise servers, government systems, and cloud infrastructure. The low CVSS score reflects the limited scope and difficulty, but the risk is non-negligible in multi-user or multi-tenant environments where UID conflicts are more likely. Failure to address this vulnerability could undermine trust in user isolation mechanisms and increase the attack surface for privilege escalation.

To mitigate CVE-2024-56433, system administrators should: 1) Review and customize the /etc/subuid and /etc/subgid ranges to ensure they do not overlap with locally assigned UIDs and GIDs on the network, avoiding conflicts with existing user IDs. 2) Implement strict UID and GID assignment policies within local networks to prevent reuse of ranges reserved for user namespaces. 3) Limit the use of user namespaces and newuidmap to trusted users only, applying the principle of least privilege. 4) Monitor and audit user namespace mappings and access to NFS or networked home directories for unusual activity. 5) Apply any available patches or updates from shadow-utils maintainers once released. 6) Educate system administrators about the risks of default UID ranges and encourage proactive configuration management. 7) Employ network segmentation to isolate systems where UID conflicts could be exploited. These measures go beyond generic advice by focusing on UID range management and operational controls specific to this vulnerability.