CVE-2025-39888: 
Linux Kernel vulnerability analysis and mitigation

A vulnerability in the Linux kernel has been identified as CVE-2025-39888, which involves a slab-out-of-bounds Write issue in the fusedevdowrite function. The vulnerability was discovered and reported by syz, and it occurs when the number of bytes to be retrieved is truncated to the upper limit by fc->maxpages in combination with an offset (NVD CVE).

The vulnerability is related to the FUSE (Filesystem in Userspace) component of the Linux kernel. The issue manifests as a slab-out-of-bounds Write condition in the fusedevdowrite function. The technical root cause involves a situation where byte retrieval is truncated to the upper limit by fc->maxpages while having an offset present. Red Hat has assigned this vulnerability a CVSS v3.1 base score of 7.0 with the vector string CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H (Red Hat CVE).

The vulnerability has been assessed with a CVSS v3.1 base score of 7.0, indicating a high severity issue. The potential impact includes the possibility of local attacks that could lead to system compromise through high-impact confidentiality, integrity, and availability breaches (Red Hat CVE).

The vulnerability has been fixed in various Linux distributions. Debian has implemented fixes across multiple versions: bullseye (5.10.237-1), bookworm (6.1.153-1), trixie (6.12.48-1), and sid (6.16.8-1). A loop termination condition has been added to prevent overruns (Debian Tracker).