---
id: "CVE-2026-99241"
kind: "vulnerability"
aliases: ["CVE-2026-99241"]
title: "Linux kernel NTFS: write faults race with truncate and fallocate"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["linux-kernel", "ntfs", "runtime", "self-hosted"]
not_affected_if: ["no-ntfs-mounts"]
published_at: "2026-11-02T16:17:49+00:00"
first_seen_at: "2026-11-02T16:24:06+00:00"
updated_at: "2026-11-02T16:26:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99241", "first_seen_at": "2026-11-02T16:24:06+00:00"}]
---

# Linux kernel NTFS: write faults race with truncate and fallocate

The Linux kernel's NTFS driver did not hold the invalidate lock during write-fault handling, so a write could race with a concurrent truncate or fallocate that is rewriting the file's cluster map. The sources do not state a concrete attacker outcome, so the impact is not established beyond a race that can corrupt file state.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the kernel is built with or loads the `ntfs` driver (NTFS, not ntfs3) with `lsmod | grep ntfs` or `grep -i ntfs /proc/filesystems`
- Check the running kernel version with `uname -r` and compare it to the fixed release in the kernel's stable branch

## Timeline

- 2026-11-02T16:24:06+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99241

## From the sources

In the Linux kernel, the following vulnerability has been resolved:

ntfs: take invalidate_lock in ntfs_filemap_page_mkwrite()

ntfs_filemap_page_mkwrite() calls iomap_page_mkwrite() without holding
mapping->invalidate_lock, so a concurrent truncate or fallocate can be
in the middle of invalidating pagecache and rewriting the runlist while
the write fault maps blocks and dirties the folio.  This races with
ntfs_attr_fallocate(), which merges clusters into the in-memory
runlist, drops the runlist lock, and only afterwards zeroes the newly
allocated clusters on disk; and with the punch-hole/insert/collapse
paths that free clusters after truncating the cache.

Per Documentation/filesystems/locking.rst, ->page_mkwrite() must ensure
there are no truncate/invalidate races, "usually mapping->invalidate_lock
is suitable for proper serialization".  xfs takes its mmaplock (= the
invalidate_lock rwsem) shared in exactly this path.

Take invalidate_lock shared around iomap_page_mkwrite().  The read-only
fault path is already covered because filemap_fault() itself grabs
invalidate_lock shared on instantiation/read paths; only page_mkwrite
was bypassing it in this driver.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_