CVE-2024-46786 is a use-after-free (UAF) vulnerability in the Linux kernel's fscache subsystem. The issue arises because the fscache_cookie_lru_timer, a timer initialized when the fscache module is inserted, is not properly deleted when the module is removed. Specifically, if the function timer_reduce() is called before the fscache module is removed, the timer is added to the timer list of the current CPU. Subsequently, after the module removal, the timer callback can still be invoked, leading to a use-after-free condition in a softIRQ context. This results in a kernel oops and a page fault due to accessing freed memory, which manifests as a supervisor read access fault in kernel mode. The vulnerability can cause system instability or crashes, as demonstrated by the kernel panic logs included in the description. The root cause is improper cleanup of kernel timers during module unload, which violates kernel memory safety principles. This vulnerability affects Linux kernel versions containing the specified commit hashes and is relevant to systems using the fscache module, which is commonly used to cache network filesystem data to improve performance. No known exploits are reported in the wild yet, and no CVSS score has been assigned. However, the vulnerability is serious due to its potential to cause denial of service via kernel crashes and possibly enable privilege escalation if exploited further.

For European organizations, this vulnerability poses a risk primarily to Linux servers and systems that utilize the fscache module, often found in environments using network filesystems such as NFS or CIFS. The impact includes potential denial of service through kernel crashes, which can disrupt critical services, especially in data centers, cloud infrastructure, and enterprise environments relying on Linux-based storage caching. While direct remote exploitation is unlikely without additional vectors, local attackers or malicious insiders could trigger the vulnerability by unloading the fscache module improperly or manipulating timer_reduce() calls. This could lead to system instability, impacting availability of services and potentially causing downtime. Given the widespread use of Linux in European government, financial, and industrial sectors, unpatched systems could face operational disruptions. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to escalate privileges or bypass security controls if combined with other exploits. The lack of a known exploit reduces immediate risk but does not eliminate the threat, especially in high-security environments where kernel integrity is critical.

Organizations should promptly apply kernel updates or patches provided by their Linux distribution vendors that address this vulnerability by ensuring proper deletion of the fscache_cookie_lru_timer during module removal. Until patches are available, administrators should avoid unloading the fscache module on production systems or ensure that timer_reduce() is not called before module removal to prevent triggering the use-after-free condition. Monitoring kernel logs for oops or page faults related to timers and the fscache module can help detect attempts to exploit this issue. Additionally, restricting local user permissions to prevent unauthorized module unloading and limiting access to systems where fscache is used can reduce risk. Employing kernel hardening techniques such as Kernel Address Sanitizer (KASAN) during testing can help identify similar issues proactively. Finally, organizations should maintain robust incident response plans to quickly address any kernel crashes or suspicious activity related to this vulnerability.