CVE-2021-46992 is a vulnerability found in the Linux kernel's netfilter nftables subsystem, specifically within the nft_hash_buckets() function. The issue arises due to improper handling of the number of hash buckets, which are stored in 32-bit variables without adequate overflow checks. This can lead to integer overflow conditions when large values are processed, as demonstrated by the syzbot fuzzing tool injecting a size value of 0x40000000 (1,073,741,824). The overflow causes undefined behavior, including a shift-out-of-bounds error detected by the Undefined Behavior Sanitizer (UBSAN) in the kernel's log2.h implementation. The vulnerability is rooted in the calculation of hash bucket sizes, where the shift exponent exceeds the limits of a 64-bit unsigned long integer, potentially leading to memory corruption or kernel crashes. The call trace indicates that the flaw occurs during the creation of new nftables sets via netfilter's nf_tables_api, triggered by netlink socket messages. Although no known exploits are reported in the wild, the vulnerability could be triggered by a local or remote attacker with the ability to send crafted netlink messages to the kernel's netfilter subsystem. This could result in denial of service (kernel panic) or potentially escalate to arbitrary code execution if exploited with additional conditions. The vulnerability affects Linux kernel versions prior to the patch that introduced proper overflow checks in nft_hash_buckets().

For European organizations, this vulnerability poses a significant risk to systems running vulnerable Linux kernel versions, especially those utilizing nftables for firewalling and network packet filtering. Many European enterprises, government agencies, and critical infrastructure providers rely on Linux-based servers and network appliances. Exploitation could lead to denial of service, disrupting business operations, critical services, or network security enforcement. In worst-case scenarios, if combined with other vulnerabilities, it could allow privilege escalation or remote code execution, compromising confidentiality and integrity of sensitive data. The impact is heightened in environments with exposed netlink interfaces or where untrusted users have local access. Given the widespread deployment of Linux in cloud infrastructure, data centers, and embedded devices across Europe, the vulnerability could affect a broad range of sectors including finance, healthcare, telecommunications, and public administration.

European organizations should prioritize updating their Linux kernel to the latest patched versions that address CVE-2021-46992. Specifically, apply vendor-supplied kernel updates or backported patches that fix the overflow checks in nft_hash_buckets(). Additionally, organizations should audit their use of nftables and netfilter configurations to minimize exposure to untrusted netlink messages. Restrict local user privileges to prevent unauthorized access to netlink sockets. Employ kernel hardening techniques such as enabling kernel lockdown modes and using security modules like SELinux or AppArmor to limit the impact of potential exploitation. Monitoring kernel logs for unusual netlink activity or kernel warnings related to nftables can provide early detection. For cloud environments, ensure that virtual machines and containers run updated kernels and that network namespaces are properly isolated. Finally, conduct penetration testing and vulnerability scanning focused on netfilter components to verify remediation.