CVE-2023-26544: Linux Kernel Use-After-Free Vulnerability

CVE-2023-26544 Overview

CVE-2023-26544 is a use-after-free vulnerability in the Linux kernel version 6.0.8. The flaw resides in the run_unpack function in fs/ntfs3/run.c, part of the NTFS3 filesystem driver. The vulnerability stems from a mismatch between the NTFS sector size and the underlying media sector size. A local authenticated attacker can trigger memory corruption by mounting or interacting with a crafted NTFS filesystem. Successful exploitation can lead to local privilege escalation, kernel memory disclosure, or denial of service. The issue is tracked under CWE-416 (Use After Free) and affects systems using the in-tree NTFS3 driver introduced in Linux 5.15.

Critical Impact

Local attackers with low privileges can trigger a kernel use-after-free in the NTFS3 driver, enabling potential privilege escalation and full compromise of confidentiality, integrity, and availability.

Affected Products

• Linux Kernel 6.0.8 (NTFS3 filesystem driver)
• Distributions shipping the in-tree NTFS3 driver prior to the upstream fix
• NetApp products incorporating affected Linux kernel versions (see NetApp Security Advisory ntap-20230316-0010)

Discovery Timeline

• 2023-02-20 - Issue discussed on the Linux Kernel Mailing List (LKML Discussion February 2023)
• 2023-02-25 - CVE-2023-26544 published to NVD
• 2023-03-16 - NetApp publishes downstream advisory
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2023-26544

Vulnerability Analysis

The vulnerability exists in the run_unpack function located in fs/ntfs3/run.c. This function parses NTFS run lists, which are compact data structures describing the on-disk layout of file extents. When the NTFS sector size declared in filesystem metadata differs from the media sector size of the underlying block device, the parsing logic can free a buffer while still retaining references to it. Subsequent operations dereference the freed memory, producing the use-after-free condition. Because the bug lives inside the kernel filesystem driver, exploitation operates in kernel context. An attacker who controls the contents of an NTFS image can manipulate run list metadata to influence allocator state after the free. This creates conditions suitable for kernel heap manipulation techniques.

Root Cause

The root cause is improper validation of sector size consistency between NTFS metadata and the backing block device. The NTFS3 driver assumes the two values match when computing buffer lifetimes during run list unpacking. When they diverge, an allocation is released along one code path while pointers to it persist along another. The upstream fix in commit 887bfc546097 corrects the size handling so that buffer lifetimes are managed consistently regardless of sector size mismatch.

Attack Vector

Exploitation requires local access with low privileges and no user interaction. An attacker supplies a maliciously crafted NTFS filesystem image, typically via a removable device, loop-mounted file, or a privileged mount helper that is reachable from an unprivileged context. When the kernel parses the run list of the crafted image, the use-after-free is triggered. On systems where automounting of removable media is enabled, the attack surface extends to anyone with physical access. Refer to the SUSE Bugzilla Report #1208697 for additional technical discussion.

Detection Methods for CVE-2023-26544

Indicators of Compromise

• Kernel oops or panic messages referencing run_unpack, fs/ntfs3/run.c, or KASAN use-after-free reports in dmesg
• Unexpected mounts of NTFS filesystems from removable devices or loop devices on servers that do not legitimately use NTFS
• Crash dumps showing tainted kernel state shortly after an NTFS mount operation

Detection Strategies

• Enable KASAN (Kernel Address Sanitizer) on test and staging kernels to surface use-after-free conditions in the NTFS3 driver before production exposure
• Audit kernel logs for module loads of ntfs3 on systems where NTFS support is not required
• Inventory running kernels against the fixed version range and flag any host still on Linux 6.0.8 with NTFS3 enabled

Monitoring Recommendations

• Forward dmesg and /var/log/kern.log to a central logging platform and alert on kernel oops messages mentioning ntfs3 or run_unpack
• Monitor mount syscall telemetry for NTFS mount events originating from non-administrative users or automount daemons
• Track udev events for removable storage attachments paired with subsequent kernel warnings

How to Mitigate CVE-2023-26544

Immediate Actions Required

• Upgrade the Linux kernel to a version containing the upstream fix from commit 887bfc546097
• Apply distribution-specific kernel updates from your vendor as soon as they are available
• Disable the ntfs3 kernel module on systems that do not require NTFS read/write support

Patch Information

The vulnerability is fixed upstream in commit 887bfc546097fbe8071dac13b2fef73b77920899 in the Linus Torvalds Linux kernel tree. Distributions including SUSE have tracked the issue under SUSE Bugzilla Report #1208697. NetApp has published downstream guidance in NetApp Security Advisory ntap-20230316-0010. Verify your running kernel includes the fix using uname -r and consult your distribution's changelog.

Workarounds

• Blacklist the NTFS3 module on systems that do not require it by adding blacklist ntfs3 to /etc/modprobe.d/
• Disable automounting of removable media and restrict mount privileges to administrative users
• Restrict physical access to systems and limit which users can attach USB storage or mount loop devices

# Configuration example: disable the ntfs3 kernel module
echo "blacklist ntfs3" | sudo tee /etc/modprobe.d/disable-ntfs3.conf
sudo rmmod ntfs3 2>/dev/null
sudo update-initramfs -u

# Verify the module is not loaded
lsmod | grep ntfs3