CVE-2026-53023 Overview
CVE-2026-53023 is an out-of-bounds read vulnerability in the Linux kernel's fs/ntfs3 filesystem driver. The flaw resides in the volume label handling logic inside ntfs_fill_super(), which converts the on-disk UTF-16 NTFS volume label to UTF-8 using utf16s_to_utf8s() and caches the result in sbi->volume.label. The conversion routine returns only the number of bytes written and does not append a NUL terminator. When the converted label fills the entire fixed-size buffer, ntfs3_label_show() reads past the end of the buffer while searching for a string terminator, leaking adjacent kernel memory into sysfs output.
Critical Impact
A local user able to mount an NTFS volume with a crafted label can trigger an out-of-bounds read in kernel memory exposed through sysfs, leading to potential information disclosure.
Affected Products
- Linux kernel versions containing the fs/ntfs3 driver
- Distributions shipping the ntfs3 in-kernel filesystem module
- Systems mounting NTFS volumes using the ntfs3 driver
Discovery Timeline
- 2026-06-24 - CVE-2026-53023 published to NVD
- 2026-06-24 - Last updated in NVD database
Technical Details for CVE-2026-53023
Vulnerability Analysis
The vulnerability is an out-of-bounds read [CWE-125] in the ntfs3 superblock initialization path. ntfs_fill_super() reads the NTFS volume label from disk as a UTF-16 string and invokes utf16s_to_utf8s() to convert it into the fixed buffer sbi->volume.label. The conversion helper returns the byte count of the converted output but does not write a trailing NUL byte. When user-space reads the label through the sysfs attribute backed by ntfs3_label_show(), the handler uses the %s format specifier, which expects a NUL-terminated C string. If the converted label exactly fills the buffer, the formatting routine continues reading past the buffer boundary until it encounters a stray zero byte in adjacent kernel memory.
The contents of the leaked bytes depend on heap layout but may include sensitive kernel data adjacent to the sbi structure. The upstream fix explicitly NUL-terminates the cached label after a successful UTF-8 conversion and clamps the exact-full case to the last byte of the buffer.
Root Cause
The root cause is missing string termination after a length-only conversion API. utf16s_to_utf8s() does not guarantee NUL termination, yet downstream consumers treat the buffer as a standard C string via %s.
Attack Vector
Exploitation requires the ability to mount a crafted NTFS volume and then read the corresponding sysfs label attribute. This typically requires local access and elevated privileges to mount, though scenarios involving automounting of removable media may broaden the attack surface. Successful exploitation results in kernel memory disclosure rather than code execution.
No synthetic exploit code is published for this issue. Refer to the upstream kernel patches for the precise fix and reachable code paths.
Detection Methods for CVE-2026-53023
Indicators of Compromise
- Unexpected reads of /sys/fs/ntfs3/*/volume_label or equivalent sysfs nodes shortly after mounting external NTFS volumes
- Mount events for NTFS volumes whose label spans the full label buffer length
- Kernel logs showing repeated ntfs3 superblock initialization from untrusted media
Detection Strategies
- Audit mount syscalls targeting the ntfs3 filesystem type and correlate with subsequent sysfs reads of label attributes
- Track the running kernel version against the patched commits referenced in upstream stable trees
- Monitor for processes outside expected administrative tooling enumerating ntfs3 sysfs attributes
Monitoring Recommendations
- Enable auditd rules for mount and umount operations involving removable media
- Centralize kernel logs and alert on ntfs3 driver messages tied to volume labels
- Inventory hosts running unpatched kernels exposing the ntfs3 driver and prioritize remediation
How to Mitigate CVE-2026-53023
Immediate Actions Required
- Apply the upstream kernel patches that NUL-terminate the cached UTF-8 volume label
- Update to a distribution kernel that incorporates the ntfs3 fix from the stable trees
- Restrict mounting of untrusted NTFS media on multi-user and server systems
Patch Information
The issue is resolved in the Linux kernel stable trees by commits 0b11fcbe80, 32b0686369, 54d564b762, 5cd0707b81, 6136bbb054, a6cd43fe9b, and bc7a0c34c4. The fix explicitly terminates sbi->volume.label after utf16s_to_utf8s() and clamps the exact-full case to the last byte of the buffer.
Workarounds
- Disable or blacklist the ntfs3 kernel module on systems that do not require NTFS access
- Restrict CAP_SYS_ADMIN and disable automatic mounting of removable NTFS media
- Remove read access to ntfs3 sysfs label attributes for non-administrative users where feasible
# Blacklist the ntfs3 module until kernel is patched
echo 'blacklist ntfs3' | sudo tee /etc/modprobe.d/blacklist-ntfs3.conf
sudo update-initramfs -u
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
