CVE-2024-56631 is a high-severity use-after-free vulnerability in the Linux kernel's SCSI generic (sg) driver, specifically in the sg_release() function. The issue arises due to improper ordering of resource cleanup and mutex unlocking. In detail, sg_release() calls kref_put(&sfp->f_ref, sg_remove_sfp) before releasing the open_rel_lock mutex. If the reference count of sfp (a structure representing the sg file pointer) reaches zero, sg_remove_sfp() is invoked, which schedules deferred work via sg_remove_sfp_usercontext() that ultimately frees sfp. However, after this kref_put() call, sg_release() continues to unlock the open_rel_lock mutex and may still reference sfp or sdp, which could have been freed already. This leads to a slab-use-after-free error, a critical memory safety flaw that can cause kernel crashes or potentially allow privilege escalation or arbitrary code execution in kernel space. The fix involves moving the kref_put() call to after the mutex unlock, ensuring no references to freed memory occur post-cleanup. This correction was validated by syzbot, an automated kernel fuzzer, confirming the elimination of the use-after-free condition. The vulnerability affects multiple Linux kernel versions identified by specific commits and has a CVSS 3.1 score of 7.8, reflecting its high impact on confidentiality, integrity, and availability with low attack complexity but requiring local privileges and no user interaction.

For European organizations, this vulnerability poses a significant risk especially to those relying on Linux-based servers, embedded systems, or infrastructure that utilize the SCSI generic driver for storage device communication. Exploitation could lead to kernel crashes causing denial of service, or more critically, local privilege escalation allowing attackers to gain root access. This can compromise sensitive data confidentiality and integrity, disrupt critical services, and facilitate further lateral movement within networks. Industries such as finance, telecommunications, healthcare, and government agencies in Europe that depend heavily on Linux servers for critical workloads are particularly vulnerable. Additionally, cloud service providers and data centers operating Linux-based infrastructure could face widespread impact if exploited. The vulnerability requires local access, so insider threats or attackers with initial footholds could leverage this flaw to escalate privileges and deepen compromise.

European organizations should prioritize patching affected Linux kernel versions by applying the official fixes that reorder the kref_put() call after mutex unlocking in sg_release(). Kernel updates from trusted Linux distributions should be deployed promptly. For systems where immediate patching is not feasible, organizations should restrict local access to trusted users only, enforce strict access controls, and monitor for unusual kernel crashes or suspicious activity indicative of exploitation attempts. Employing kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and enabling security modules like SELinux or AppArmor can reduce exploitation risk. Additionally, organizations should audit and limit the use of the SCSI generic driver where possible and maintain comprehensive logging and alerting to detect anomalous behavior. Regular vulnerability scanning and penetration testing focusing on local privilege escalation vectors will help identify exposure.