CVE-2024-27396 is a use-after-free vulnerability identified in the Linux kernel's GPRS Tunneling Protocol (GTP) implementation, specifically within the gtp_dellink function. The vulnerability arises due to improper handling of Read-Copy-Update (RCU) synchronization primitives during the traversal of a linked list. The function call_rcu is invoked inside the hlist_for_each_entry_rcu loop, but it is not enclosed within an RCU read-side critical section. This design flaw allows the RCU grace period to elapse while the traversal is ongoing, potentially leading to the premature freeing of a key data structure that is still being accessed. Consequently, this can result in a use-after-free condition, which is a memory safety error where the kernel accesses memory that has already been freed. The fix involves replacing the traversal macro hlist_for_each_entry_rcu with hlist_for_each_entry_safe, which ensures safe iteration by allowing the current element to be safely removed or freed during traversal without causing invalid memory access. This vulnerability affects multiple versions of the Linux kernel as indicated by the affected commit hashes, and it was publicly disclosed on May 9, 2024. There are no known exploits in the wild at the time of publication, and no CVSS score has been assigned yet. The vulnerability is significant because the GTP protocol is widely used in mobile networks for tunneling user data and signaling between network nodes, making the kernel component critical for telecommunications infrastructure and other systems relying on Linux networking stacks.

For European organizations, the impact of CVE-2024-27396 could be substantial, especially for those operating telecommunications infrastructure, mobile network operators, and enterprises using Linux-based systems for network routing or mobile data processing. Exploitation of this vulnerability could lead to kernel crashes, denial of service, or potentially privilege escalation if an attacker can execute arbitrary code in kernel space due to the use-after-free condition. This could disrupt critical services, including mobile communications and data services, affecting both service providers and end-users. Additionally, organizations relying on Linux servers for network functions or embedded devices in industrial or IoT environments may face increased risk. The absence of known exploits currently reduces immediate risk, but the vulnerability's nature and the critical role of the Linux kernel in network operations mean that attackers could develop exploits in the future. European organizations must consider the potential for service outages, data confidentiality breaches, and integrity compromises in their risk assessments.

To mitigate CVE-2024-27396, European organizations should promptly apply the official Linux kernel patches that replace the unsafe traversal macro with the safe variant (hlist_for_each_entry_safe) in the gtp_dellink function. Kernel updates should be prioritized on all systems running affected Linux kernel versions, especially those involved in mobile network operations or handling GTP traffic. Organizations should also audit their network infrastructure to identify devices and servers using vulnerable kernel versions. Employing kernel live patching solutions where available can reduce downtime during patch deployment. Additionally, network segmentation and strict access controls should be enforced to limit exposure of vulnerable systems to untrusted networks. Monitoring kernel logs and network traffic for anomalies related to GTP traffic may help detect attempted exploitation. Finally, organizations should maintain an up-to-date inventory of Linux kernel versions in use and subscribe to security advisories to ensure timely awareness of new patches or exploit developments.