CVE-2022-49776 is a vulnerability identified in the Linux kernel's macvlan network driver component. The macvlan driver allows the creation of virtual network interfaces that share a physical network interface, commonly used for network isolation and virtualization purposes. The vulnerability arises from the lack of enforcement of a consistent minimal MTU (Maximum Transmission Unit) size during the creation and configuration of macvlan interfaces. Specifically, the macvlan driver should enforce a minimal MTU of 68 bytes, but prior to the patch, it allowed setting MTU values below this threshold. This improper MTU configuration can lead to instability and crashes in the IPv6 network stack when the affected macvlan link is brought up. The issue manifests when an administrator or automated process attempts to create or modify a macvlan interface with an MTU smaller than 68 bytes, which is below the minimal acceptable size for IPv6 packets. The patch enforces this minimal MTU at link creation and during MTU changes, preventing the interface from being configured with an MTU less than 68 bytes. Attempts to set an MTU below this threshold now result in errors, thereby avoiding the kernel crashes caused by malformed packet handling in the IPv6 stack. This vulnerability is rooted in kernel-level network interface configuration and affects all Linux kernel versions prior to the patch that do not enforce this minimal MTU constraint on macvlan interfaces. There are no known exploits in the wild at this time, and no CVSS score has been assigned. The vulnerability primarily impacts network stability and availability rather than confidentiality or integrity, as it can cause denial of service conditions through kernel crashes triggered by invalid MTU settings on macvlan interfaces.

For European organizations, this vulnerability poses a risk primarily to network infrastructure stability and availability. Organizations utilizing Linux-based systems with macvlan interfaces—common in data centers, cloud environments, and virtualized network setups—may experience kernel crashes leading to service interruptions if an attacker or misconfigured system sets an MTU below the minimal threshold. Although exploitation requires the ability to create or modify macvlan interfaces, which typically requires administrative privileges, insider threats or compromised systems could trigger this condition. The impact is more pronounced in environments heavily reliant on IPv6 networking, as the crash occurs in the IPv6 stack. Disruptions could affect critical services, virtualized network functions, and containerized workloads that depend on macvlan interfaces for network segmentation. While no direct data breach or privilege escalation is indicated, the denial of service potential could affect operational continuity, especially in sectors such as finance, telecommunications, and critical infrastructure prevalent in Europe. The absence of known exploits reduces immediate risk, but unpatched systems remain vulnerable to accidental misconfiguration or targeted attacks by privileged adversaries.

European organizations should apply the official Linux kernel patches that enforce the minimal MTU of 68 bytes on macvlan interfaces as soon as they become available. Until patches are deployed, administrators should implement strict configuration management and monitoring to prevent the creation or modification of macvlan interfaces with MTU values below 68 bytes. Network management tools and automation scripts should be audited and updated to enforce MTU constraints. Additionally, limit administrative access to systems capable of creating macvlan interfaces to trusted personnel only, and employ role-based access controls to reduce the risk of accidental or malicious misconfiguration. Monitoring kernel logs and network interface configurations for unusual MTU settings can provide early detection of attempts to exploit this vulnerability. For environments using IPv6 extensively, consider additional network segmentation and redundancy to mitigate potential service disruptions. Finally, maintain up-to-date backups and incident response plans to recover quickly from any denial of service incidents caused by this vulnerability.