CVE-2026-74307

Received Received - Intake

EXT4 Filesystem Validation Bypass in Linux Kernel

Publication date: 2026-08-15

Last updated on: 2026-08-17

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: ext4: validate donor file superblock early in EXT4_IOC_MOVE_EXT Reject the EXT4_IOC_MOVE_EXT ioctl early if the donor file does not belong to the same superblock as the original file. Currently, this validation is performed inside ext4_move_extents() by mext_check_validity(), but only after lock_two_nondirectories() has already acquired the inode locks. When the donor fd refers to a file on a different filesystem (e.g., overlayfs), this late validation creates a circular lock dependency: CPU0 (overlayfs write) CPU1 (ext4 ioctl) ---- ---- inode_lock(ovl_inode) mnt_want_write_file(filp) sb_start_write(ext4_sb) [sb_writers] backing_file_write_iter() vfs_iter_write(real_file) file_start_write(real_file) sb_start_write(ext4_sb) [blocked by freeze] lock_two_nondirectories() inode_lock(ovl_inode) [blocked] With a concurrent freeze operation holding sb_writers write side, this forms a deadlock cycle: CPU0 waits for freeze to complete, freeze waits for CPU1's sb_writers reader to exit, CPU1 waits for CPU0's inode lock. Since EXT4_IOC_MOVE_EXT exchanges physical extents between two files, it fundamentally requires both files to reside on the same ext4 filesystem. Moving the superblock check before any lock acquisition is both semantically correct and eliminates the circular dependency by ensuring that cross-filesystem donor fds are rejected before sb_writers or inode locks are taken.

CVSS Scores

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Meta Information

Published

2026-08-15

Last Modified

2026-08-17

Generated

2026-09-04

AI Q&A

2026-08-15

EPSS Evaluated

2026-09-03

NVD

CVE-2026-74307

EUVD

EUVD-2026-59454

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves a deadlock issue in the EXT4_IOC_MOVE_EXT ioctl operation. The problem occurs when the donor file for an extent move operation is on a different filesystem, such as overlayfs, compared to the original file. The validation to check if both files belong to the same superblock was happening too late, after locks were acquired, leading to a circular dependency and potential system hang.

Detection Guidance

This vulnerability is specific to the Linux kernel's EXT4 filesystem and involves the EXT4_IOC_MOVE_EXT ioctl operation. Detection requires checking for kernel versions affected by this issue and monitoring for potential deadlock conditions during filesystem operations.

Impact Analysis

This vulnerability can cause a system deadlock, where the kernel becomes unresponsive. If an attacker triggers the EXT4_IOC_MOVE_EXT ioctl with a donor file on a different filesystem, the system may freeze, requiring a reboot to recover. This can lead to denial of service and potential data loss.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA as it is a Linux kernel filesystem issue unrelated to data privacy or security controls required by these regulations.

Mitigation Strategies

Apply the latest Linux kernel patches that address this vulnerability. Avoid using the EXT4_IOC_MOVE_EXT ioctl operation until the patch is applied. Monitor system logs for deadlock warnings or filesystem errors.

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