CVE-2025-68368 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
md: init bioset in mddev_init
IO operations may be needed before md_run(), such as updating metadata after writing sysfs. Without bioset, this triggers a NULL pointer dereference as below:
BUG: kernel NULL pointer dereference, address: 0000000000000020 Call Trace: md_update_sb+0x658/0xe00 new_level_store+0xc5/0x120 md_attr_store+0xc9/0x1e0 sysfs_kf_write+0x6f/0xa0 kernfs_fop_write_iter+0x141/0x2a0 vfs_write+0x1fc/0x5a0 ksys_write+0x79/0x180 __x64_sys_write+0x1d/0x30 x64_sys_call+0x2818/0x2880 do_syscall_64+0xa9/0x580 entry_SYSCALL_64_after_hwframe+0x4b/0x53
Reproducer ``` mdadm -CR /dev/md0 -l1 -n2 /dev/sd[cd]
echo inactive > /sys/block/md0/md/array_state echo 10 > /sys/block/md0/md/new_level ```
mddev_init() can only be called once per mddev, no need to test if bioset has been initialized anymore.
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Analysis
by VulDB Data Team • 12/29/2025
This vulnerability exists in the Linux kernel's md (multiple device) subsystem where a null pointer dereference occurs during metadata update operations. The issue stems from improper initialization of the bioset structure within the mddev_init function, which is critical for handling I/O operations in software RAID configurations. When the mdadm utility creates a RAID array and subsequently attempts to modify array state through sysfs interface, the kernel fails to properly initialize the bioset before performing I/O operations, leading to a kernel panic.
The technical flaw manifests when IO operations are required before the md_run() function executes, particularly during metadata updates triggered by sysfs writes. The specific call trace reveals that the error originates from md_update_sb function which attempts to access a NULL bioset pointer when updating superblock metadata. This occurs because the bioset initialization check fails to properly handle cases where I/O operations are needed prior to the standard md_run() sequence, creating a race condition or initialization order issue.
The operational impact of this vulnerability is significant as it can cause complete system crashes when legitimate RAID management operations are performed through sysfs interfaces. Attackers could potentially exploit this by crafting specific sequences of sysfs writes that trigger the NULL pointer dereference, leading to denial of service conditions. The vulnerability affects any Linux system running kernel versions with the affected md subsystem code, particularly those managing software RAID arrays through mdadm or direct sysfs manipulation.
The root cause aligns with CWE-476 Null Pointer Dereference, where a pointer expected to reference valid memory is NULL during access. This vulnerability also maps to ATT&CK technique T1490 for creating or deploying malicious code and T1566 for malicious code injection, as it enables potential exploitation for system disruption. The issue specifically relates to improper initialization of kernel data structures and inadequate error handling in the md subsystem's initialization flow.
Mitigation strategies include applying the kernel patch that ensures bioset initialization occurs properly before any I/O operations are attempted. System administrators should update to kernel versions containing the fix immediately, as the vulnerability can be triggered through standard RAID management operations. Additionally, monitoring for sysfs write operations on md devices and implementing proper error handling in management scripts can help detect and prevent exploitation attempts. The fix involves modifying mddev_init to ensure bioset is always properly initialized regardless of the operational sequence, eliminating the need for redundant initialization checks that can lead to the NULL pointer condition.