CVE-2025-39743

Vulnerability

Overview

A vulnerability in the Linux kernel's JFS filesystem occurs when an inode with a hard link count of 0 is evicted. The fileset value of the inode, read from disk, is AGGR_RESERVED_I. During eviction, because the hard link count is 0, the inode's pages are not truncated. This leaves nrpages greater than 0, which triggers a BUG_ON assertion in clear_inode(), causing a kernel panic [1].

Exploitation

An attacker who can mount a corrupted JFS filesystem or trigger a scenario where an inode's hard link count becomes 0 without proper page truncation can cause a denial of service. No special privileges are required beyond the ability to access the filesystem. The attack is local, as it involves mounting a crafted filesystem image.

Impact

Successful exploitation results in a kernel panic, leading to a denial of service (system crash). The vulnerability is classified as high severity with a CVSS v3 score of 7.8, reflecting the potential for complete system unavailability.

Mitigation

Patches have been applied to the Linux kernel stable branches [2][3][4]. Users should update to the latest kernel versions containing the fix. Affected products include SIMATIC CN 4100 versions prior to V5.0, where this CVE is listed among others [1].