CVE-2024-27394 is a high-severity use-after-free vulnerability identified in the Linux kernel's TCP implementation, specifically within the tcp_ao_connect_init function. The root cause lies in the improper handling of Read-Copy-Update (RCU) synchronization during the traversal of a linked list using hlist_for_each_entry_rcu. The function call_rcu, which defers freeing memory until after an RCU grace period, is invoked outside of an RCU read-side critical section. This timing flaw allows the grace period to elapse while the traversal is still ongoing, leading to the possibility that the memory (key) being accessed is freed prematurely. Consequently, this results in a use-after-free condition (CWE-416), which can cause memory corruption, crashes, or potentially arbitrary code execution. The fix involves replacing the traversal macro with hlist_for_each_entry_safe, which ensures safe iteration by protecting against concurrent modifications and premature freeing of list elements. The vulnerability affects specific Linux kernel versions identified by commit hashes 7c2ffaf21bd67f73d21560995ce17eaf5fc1d37f. The CVSS v3.1 base score is 7.4, reflecting high severity with a vector indicating local attack vector (AV:L), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). There are no known exploits in the wild at the time of publication (May 9, 2024). This vulnerability is critical for systems relying on the affected Linux kernel versions, especially those handling TCP connections in environments where local users or processes could trigger the flaw.

For European organizations, the impact of CVE-2024-27394 can be significant, particularly in sectors relying heavily on Linux-based infrastructure such as telecommunications, finance, government, and cloud service providers. The vulnerability's ability to cause memory corruption and potentially allow arbitrary code execution could lead to system crashes, denial of service, or unauthorized privilege escalation. This could disrupt critical services, compromise sensitive data, and undermine operational continuity. Given the high confidentiality, integrity, and availability impacts, exploitation could facilitate lateral movement within networks or persistent footholds for attackers. Although exploitation requires local access and has high complexity, insider threats or compromised local accounts could leverage this vulnerability. European organizations with multi-tenant cloud environments or shared hosting services are particularly at risk if kernel versions are unpatched. Additionally, the lack of user interaction needed for exploitation increases the risk in automated or unattended systems. The absence of known exploits currently provides a window for proactive mitigation, but the high severity score necessitates urgent patching to prevent future attacks.

European organizations should prioritize patching affected Linux kernel versions immediately by applying the official fixes that replace the unsafe list traversal with safe iteration mechanisms. System administrators must verify kernel versions in use and upgrade to patched releases or backport the fix if using long-term support kernels. Employ kernel hardening techniques such as enabling Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and other memory protection features to reduce exploitation likelihood. Restrict local user access to trusted personnel and enforce strict privilege separation to minimize the risk of local exploitation. Implement continuous monitoring for unusual kernel behavior or crashes that may indicate exploitation attempts. For environments where immediate patching is not feasible, consider isolating vulnerable systems or limiting local user capabilities through mandatory access controls (e.g., SELinux, AppArmor). Regularly audit and update system software to maintain security posture. Finally, maintain an incident response plan tailored to kernel-level vulnerabilities to quickly address potential exploitation.