CVE-2026-53027: Linux NTFS3 Kernel Denial-of-Service Vulnerability

Technical summary

CVE-2026-53027 is a local denial-of-service vulnerability in fs/ntfs3's attr_data_get_block_locked() function. When a compressed or sparse attribute undergoes frame-alignment cluster rounding using cmask, vcn may differ from vcn0. The existing code loads runs for the vcn segment but omits loading runs for vcn0 when vcn0 resides in a different attribute segment. Consequently, run_lookup_entry(vcn0) returns SPARSE_LCN due to the unloaded segment, triggering a WARN_ON(1) condition. The fix adds a segment boundary check for vcn0 post-vcn validation, ensuring the appropriate attribute segment is located and loaded into the in-memory run list before run lookup occurs.

Business impact

Systems running vulnerable Linux kernels with NTFS3 support face local denial-of-service risk. Exploitation requires local access and occurs during normal filesystem operations on compressed or sparse NTFS files meeting specific alignment criteria. While remote code execution is not possible, successful exploitation can crash the kernel, causing service interruptions. Organizations relying on NTFS3 for interoperability with Windows systems—particularly in virtual environments, containers, or workstations—should prioritize patching to maintain availability and system stability.

Affected systems

The Linux kernel, specifically the NTFS3 filesystem driver component, is affected. Vulnerable systems include any Linux installation with NTFS3 support enabled that processes compressed or sparse NTFS file attributes. This includes both desktop Linux distributions and server environments using NTFS3. The vulnerability requires local filesystem access to trigger, limiting its scope to authenticated users or those with physical access to the system.

Exploitability

Exploitability is low to moderate. An attacker requires local system access and must trigger specific filesystem operations on compressed or sparse NTFS attributes with frame-aligned cluster characteristics. Exploitation is not remotely possible and does not grant privilege escalation. However, any local user capable of accessing the filesystem can potentially trigger the condition through normal file operations, making it a concern in multi-user systems, shared hosting environments, or systems where local access is readily available.

Remediation

Apply the Linux kernel patch resolving CVE-2026-53027. The fix modifies attr_data_get_block_locked() to add a segment boundary check for vcn0, ensuring its runs are loaded before run_lookup_entry() is called. Verify the patch version against the official Linux kernel advisory and your distribution's security bulletins, as backport availability and version numbers vary by vendor. Recompile and deploy the updated kernel, followed by system reboot.

Patch guidance

Check your Linux distribution's security advisory for the specific patched kernel version addressing CVE-2026-53027. Canonical, Red Hat, SUSE, Debian, and other distributors will release updates through their respective repositories. Install the latest kernel update available for your distribution, verify the patch is included using kernel release notes or changelog, and reboot. Organizations using custom kernels should apply the upstream fix directly to their build tree. Verify NTFS3 module is properly rebuilt post-patching.

Detection guidance

Monitor system logs for WARN_ON(1) messages originating from fs/ntfs3's attr_data_get_block_locked() function, typically appearing in dmesg or kernel ring buffer as a kernel warning. Enable kernel debugging symbols if necessary to correlate warnings with this specific code path. Track kernel crash reports or unexpected reboots coinciding with NTFS3 filesystem operations on compressed or sparse files. In containerized or virtualized environments, monitor host kernel logs for these warnings even if individual containers appear unaffected. Correlate events with filesystem access patterns involving NTFS volumes.

Why prioritize this

While the CVSS 3.1 score of 5.5 (Medium) reflects local-only access requirements and no confidentiality or integrity impact, this vulnerability should be prioritized for systems actively using NTFS3. The availability impact is significant—kernel crashes interrupt services—and the attack surface includes any local user with filesystem access. Organizations supporting NTFS interoperability or running NTFS3 in production should patch promptly. Systems without NTFS3 enabled can safely defer this update unless NTFS3 is planned for deployment.

Risk score, explained

The CVSS 3.1 score of 5.5 reflects the vulnerability's Medium severity based on: (1) Attack Vector: Local—requiring system or container access; (2) Attack Complexity: Low—normal filesystem operations suffice; (3) Privileges Required: Low—any local user can trigger the condition; (4) User Interaction: None; (5) Scope: Unchanged; (6) Confidentiality: None; (7) Integrity: None; (8) Availability: High—kernel crash or instability. The score appropriately captures the local DoS nature without privilege escalation or data exposure potential.

Frequently asked questions