CVE-2024-38626 is a vulnerability identified in the Linux kernel's FUSE (Filesystem in Userspace) subsystem. The issue arises from improper handling of the FR_SENT flag when re-adding requests into the pending list during FUSE operations. Specifically, the vulnerability manifests when a FUSE_NOTIFY_RESEND notification is sent by the write() syscall, causing all processing requests to be resent. During this process, the INIT request is moved from the processing list back to the pending list without clearing the FR_SENT bit. Subsequent attempts to read this request with an invalid output address cause the request to be ended prematurely, triggering a kernel warning in fuse_request_end(). This improper state management can lead to kernel warnings and potentially unstable kernel behavior. The root cause is the failure to clear the FR_SENT flag when re-adding requests, which the patch addresses by ensuring this flag is cleared appropriately. The vulnerability was reported by Lee Bruce and affects Linux kernel versions including the 6.9.0-rc7 release candidate. Although no known exploits are currently reported in the wild, the issue could be triggered by malicious or malformed FUSE filesystem operations, potentially leading to denial of service or kernel instability.

For European organizations relying on Linux systems with FUSE filesystems—commonly used for mounting user-space filesystems such as SSHFS, cloud storage mounts, or custom filesystem implementations—this vulnerability could lead to system instability or crashes. While it does not directly indicate privilege escalation or arbitrary code execution, the kernel warnings and potential crashes could disrupt critical services, especially in environments where FUSE is heavily utilized for storage or network filesystem access. This could impact availability of services, data access, and operational continuity. Organizations running containerized workloads or virtualized environments on Linux hosts using FUSE may also experience disruptions. Given the widespread use of Linux in European data centers, cloud providers, and enterprise infrastructure, the vulnerability poses a moderate risk to service reliability and uptime if exploited or triggered inadvertently.

To mitigate this vulnerability, European organizations should prioritize applying the official Linux kernel patches that clear the FR_SENT flag when re-adding requests to the pending list in the FUSE subsystem. Kernel upgrades to versions including this fix (post-6.9.0-rc7 stable releases) are recommended. In environments where immediate patching is not feasible, organizations should audit and restrict usage of FUSE filesystems to trusted users and applications only, minimizing exposure to untrusted or malformed FUSE requests. Monitoring kernel logs for fuse_request_end warnings can help detect attempts to trigger the issue. Additionally, implementing strict access controls and sandboxing for processes interacting with FUSE filesystems can reduce the risk of exploitation. For cloud and container environments, ensure host kernel versions are updated and consider disabling unnecessary FUSE mounts to reduce attack surface.