ntfs: fix race between fallocate and mmap reads
The NTFS driver in the Linux kernel ran standard fallocate modes without invalidate_lock before the fix, so concurrent mmap reads could see old disk contents. No fixed version is listed yet.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- No fix listed
- Who is exposed
- Not reported
Do first: Workaround: The sources give no workaround. Limiting concurrent fallocate and mmap use on NTFS files would reduce exposure, but no source confirms this as a mitigation.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 25/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: ntfs: fix race between fallocate and mmap reads The fallocate implementation only takes invalidate_lock for punch hole, collapse range, and insert range operations. For standard allocation modes (mode == 0, FALLOC_FL_KEEP_SIZE), the lock is not held. During ntfs_attr_fallocate(), new clusters are mapped to the runlist via ntfs_attr_map_cluster() before being zeroed by ntfs_dio_zero_range(). This creates a window where concurrent mmap page faults can read uninitialized disk data. Since mmap uses filemap_fault() which takes invalidate_lock in shared mode, it can fault in pages during this window and expose old disk contents to userspace. This is an information leak and data integrity issue. Fix by taking invalidate_lock for all fallocate operations, not just for punch/collapse/insert modes. This prevents concurrent page faults from accessing unzeroed clusters during the allocation window.
What to do
Workaround: The sources give no workaround. Limiting concurrent fallocate and mmap use on NTFS files would reduce exposure, but no source confirms this as a mitigation.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- Linux Linux
Version range not reported
- Linux Linux
7.1
Evidence 2
- Link
- Link
Corrections
None so far.
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Questions about CVE-2026-99242
What does this mean?
During an fallocate allocation on an NTFS file, a concurrent mmap page fault can read old, uninitialized contents from disk. This can expose that data to userspace, which is both an information leak and a data integrity problem.Source: git.kernel.org
Am I affected, and how do I check?
The issue is in the Linux kernel's NTFS driver before the fix, in the standard fallocate modes (mode 0 or FALLOC_FL_KEEP_SIZE) when mmap reads of the same file run concurrently. The sources do not list specific kernel version numbers, so check whether your kernel includes the fix commit for this CVE.Source: git.kernel.org
What should I do about it?
The sources do not name a fixed kernel version. Install the kernel update from your distribution or vendor once it includes the fix for CVE-2026-99242.Source: git.kernel.org
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What if there's no patch?
The sources give no workaround. Limiting concurrent fallocate and mmap use on NTFS files would reduce exposure, but no source confirms this as a mitigation.Source: git.kernel.org