CVE-2024-27020 is a high-severity vulnerability in the Linux kernel's netfilter subsystem, specifically within the nftables framework. The vulnerability arises from a potential data race condition in the function __nft_expr_type_get(). The root cause is that the function nft_unregister_expr() can execute concurrently with __nft_expr_type_get(), and there is no synchronization or protection when iterating over the nf_tables_expressions linked list in __nft_expr_type_get(). This lack of concurrency control can lead to a data race on the nf_tables_expressions list entries, potentially causing memory corruption, use-after-free, or other undefined behaviors. The fix involves using list_for_each_entry_rcu() to safely iterate over the nf_tables_expressions list with Read-Copy-Update (RCU) synchronization primitives, and applying rcu_read_lock() in the caller function nft_expr_type_get() to protect the entire type query process. This ensures safe concurrent access and prevents the race condition. The vulnerability is tracked under CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization) and has a CVSS v3.1 score of 7.0, indicating high severity. The attack vector is local (AV:L), requiring low privileges (PR:L), no user interaction (UI:N), and impacts confidentiality, integrity, and availability (C:H/I:H/A:H). No known exploits are currently reported in the wild. The affected versions are specific Linux kernel commits identified by the hash ef1f7df9170dbd875ce198ba84e6ab80f6fc139e, indicating a particular kernel version or patch level. This vulnerability is significant because nftables is widely used for packet filtering and firewalling in Linux systems, and a data race here could be exploited to cause kernel crashes, privilege escalation, or arbitrary code execution in the kernel context.

For European organizations, the impact of CVE-2024-27020 can be substantial, especially for those relying on Linux-based infrastructure for critical network functions such as firewalls, routers, and security appliances. Exploitation of this vulnerability could lead to kernel crashes (denial of service), unauthorized privilege escalation, or compromise of system integrity, potentially allowing attackers to bypass security controls or disrupt network traffic filtering. This can affect confidentiality by exposing sensitive network data, integrity by allowing unauthorized modifications, and availability by causing system outages. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure, which heavily depend on Linux servers and network security devices, are at higher risk. The local attack vector means that attackers need some level of access to the system, which could be achieved through compromised user accounts or insider threats. Given the widespread use of Linux in European data centers and enterprise environments, unpatched systems could become targets for attackers aiming to disrupt operations or gain deeper access to networks.

1. Immediate patching: Apply the official Linux kernel patches that address CVE-2024-27020 as soon as they are available from trusted sources or Linux distribution vendors. 2. Kernel version management: Ensure that all Linux systems, especially those running nftables for firewalling, are updated to kernel versions that include the fix. 3. Access control: Restrict local access to Linux systems to trusted users only, minimizing the risk of local exploitation. 4. Monitoring and auditing: Implement monitoring for unusual kernel crashes or nftables-related errors that could indicate exploitation attempts. 5. Harden user privileges: Limit the number of users with low-level privileges that could trigger this vulnerability and enforce strict privilege separation. 6. Use security modules: Employ Linux Security Modules (e.g., SELinux, AppArmor) to restrict kernel module interactions and reduce the attack surface. 7. Network segmentation: Isolate critical Linux systems running nftables in secure network segments to limit lateral movement in case of compromise. 8. Incident response readiness: Prepare for rapid response in case exploitation is detected, including system isolation and forensic analysis.