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 6.0.8 affecting the NTFS3 file system driver. The flaw exists in the run_unpack function within fs/ntfs3/run.c and is triggered by a mismatch between NTFS sector size and media sector size. This memory corruption vulnerability can allow a local attacker with low privileges to potentially execute arbitrary code or cause system instability.

Critical Impact

Local attackers with low privileges can exploit this use-after-free condition to achieve high impact on system confidentiality, integrity, and availability, potentially leading to privilege escalation or arbitrary code execution.

Affected Products

• Linux Kernel 6.0.8
• Linux Kernel versions with NTFS3 driver enabled
• Systems mounting NTFS file systems with mismatched sector sizes

Discovery Timeline

• 2023-02-25 - CVE-2023-26544 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2023-26544

Vulnerability Analysis

This use-after-free vulnerability resides in the NTFS3 file system driver, specifically within the run_unpack function in fs/ntfs3/run.c. The vulnerability is classified as CWE-416 (Use After Free), which occurs when a program continues to use memory after it has been freed.

The root cause stems from improper handling of sector size differences between the NTFS file system and the underlying media. When the NTFS sector size differs from the media sector size, the code path in run_unpack can access memory that has already been freed, leading to undefined behavior.

This type of memory corruption vulnerability is particularly dangerous in kernel space, as successful exploitation could allow an attacker to escalate privileges, execute arbitrary code with kernel privileges, or cause a denial of service condition through system crash.

Root Cause

The vulnerability originates from inadequate bounds checking and memory lifecycle management when the run_unpack function processes NTFS run lists. When there is a discrepancy between the NTFS sector size configuration and the actual media sector size, the function may reference memory objects that have been deallocated. This race between memory deallocation and subsequent access creates the use-after-free condition.

Attack Vector

The attack requires local access to the system with low privileges. An attacker could craft a malicious NTFS volume or manipulate an existing one to trigger the sector size mismatch condition. When the vulnerable system mounts or accesses the crafted file system, the run_unpack function processes the malformed data, triggering the use-after-free condition.

The exploitation scenario involves:

1. Creating or modifying an NTFS volume with specific sector size configurations
2. Having the target system mount or access the malicious volume
3. Triggering the code path in run_unpack that processes the mismatched sector sizes
4. Exploiting the use-after-free to gain code execution or cause system instability

Technical details of the vulnerability and the fix can be found in the Linux Kernel Commit #887bfc546097 and the Linux Kernel Mailing List Post.

Detection Methods for CVE-2023-26544

Indicators of Compromise

• Unexpected kernel crashes or panics when mounting NTFS volumes
• Suspicious NTFS volumes with unusual sector size configurations
• System instability following NTFS file system access operations
• Kernel log entries indicating memory corruption in fs/ntfs3/run.c

Detection Strategies

• Monitor kernel logs for NTFS3 driver errors and memory-related warnings
• Implement file system monitoring to detect mounting of untrusted NTFS volumes
• Deploy kernel address sanitizer (KASAN) in development environments to detect use-after-free conditions
• Audit system access to external storage devices and removable media

Monitoring Recommendations

• Configure kernel logging to capture NTFS3 driver warnings and errors at verbose levels
• Implement endpoint detection rules for unexpected kernel module behavior
• Monitor for privilege escalation attempts following NTFS file system operations
• Enable SentinelOne kernel-level monitoring for memory corruption detection

How to Mitigate CVE-2023-26544

Immediate Actions Required

• Update to a patched Linux kernel version that addresses this vulnerability
• Restrict mounting of untrusted NTFS volumes on vulnerable systems
• Disable NTFS3 kernel module if not required for operations
• Implement strict access controls for removable media and external storage

Patch Information

The vulnerability has been addressed in the upstream Linux kernel. The fix is available in commit 887bfc546097fbe8071dac13b2fef73b77920899 in the mainline kernel repository. System administrators should update to kernel versions that include this patch.

For enterprise Linux distributions, consult your vendor's security advisories:

• SUSE Bug Report #1208697
• NetApp Security Advisory NTAP-20230316-0010

Workarounds

• Disable the NTFS3 kernel module using modprobe -r ntfs3 if NTFS support is not required
• Implement mount restrictions using /etc/fstab and mount policies to prevent untrusted NTFS volumes
• Use application-level NTFS implementations (ntfs-3g via FUSE) as an alternative to the kernel driver
• Implement strict physical access controls to prevent connection of malicious storage devices

# Disable NTFS3 kernel module
sudo modprobe -r ntfs3

# Blacklist NTFS3 module to prevent automatic loading
echo "blacklist ntfs3" | sudo tee /etc/modprobe.d/blacklist-ntfs3.conf

# Verify module is not loaded
lsmod | grep ntfs3