CVE-2024-47691 is a use-after-free vulnerability in the Linux kernel's F2FS (Flash-Friendly File System) implementation, specifically within the f2fs_stop_gc_thread() function. The flaw arises from a race condition involving the garbage collection thread pointer (sbi->gc_th). The vulnerability occurs when the filesystem is remounted or shut down, where two concurrent paths can invoke f2fs_do_shutdown(): one via f2fs_ioc_shutdown() and another via f2fs_shutdown(). The issue is that in the f2fs_ioc_shutdown() path, the necessary sb->s_umount semaphore is not held, leading to a race condition where the garbage collection thread pointer can be freed (kfree(gc_th)) and set to NULL while still being accessed. This results in a use-after-free condition, which can cause kernel crashes or potentially allow attackers to execute arbitrary code or escalate privileges by manipulating kernel memory. The vulnerability was identified by syzbot and fixed by ensuring the sb->s_umount semaphore is acquired during the f2fs_ioc_shutdown() path, preventing concurrent access and eliminating the race condition. The vulnerability affects Linux kernel versions containing the specified commit (7950e9ac638e84518fbdd5c930939ad46a1068c5) and is relevant to systems using the F2FS filesystem, commonly deployed on flash storage devices. No known exploits are reported in the wild as of the publication date (October 21, 2024).

For European organizations, this vulnerability poses a significant risk primarily to systems running Linux with F2FS filesystems, which are often used in embedded systems, mobile devices, and some server environments utilizing flash storage. Exploitation could lead to denial of service through kernel crashes or potentially privilege escalation if an attacker can trigger the use-after-free condition. This could compromise confidentiality, integrity, and availability of affected systems. Organizations relying on Linux-based infrastructure for critical services, especially those with flash storage using F2FS, could face operational disruptions or security breaches. Given the kernel-level nature of the vulnerability, successful exploitation could undermine system security controls and lead to broader network compromise. The lack of known exploits currently reduces immediate risk, but the vulnerability's presence in widely used Linux kernels means European entities should prioritize patching to mitigate future threats.

European organizations should immediately identify Linux systems using the F2FS filesystem and verify kernel versions against the fixed commit. Applying the latest Linux kernel patches that address CVE-2024-47691 is critical. For systems where immediate patching is not feasible, organizations should limit access to affected systems, especially restricting untrusted users from performing remount or shutdown operations on F2FS filesystems. Monitoring kernel logs for unusual crashes or stack traces related to f2fs_stop_gc_thread can help detect exploitation attempts. Additionally, implementing strict access controls and employing kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) can reduce exploitation likelihood. Organizations should also review and update incident response plans to address potential kernel-level compromises. Finally, coordinating with Linux distribution vendors for timely updates and advisories is recommended.