# CVE-2026-90131: ntfs: serialize resident iomap reads with mrec_lock

> A race condition in the Linux kernel NTFS driver allows attackers to read torn data or cause a denial of service via concurrent file operations.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-90131, GHSA-p65r-ghh2-3f2q, UBUNTU-CVE-2026-90131

## What is CVE-2026-90131?

CVE-2026-90131 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

ntfs: serialize resident iomap reads with mrec_lock

ntfs_read_iomap_begin_resident() walks the MFT record through
ntfs_attr_lookup() -> ntfs_attr_find() without taking ni->mrec_lock,
while ntfs_attr_record_resize(), ntfs_make_room_for_attr() and
ntfs_resident_attr_record_add() memmove() the same base_ni->mrec buffer
under that lock. map_mft_record() only takes a reference and does not
serialize, so the reader can observe torn attribute length and offset
fields while a writer is relocating the records.

KCSAN reports the race between the mmap read fault path and both link()
and unlink():

  BUG: KCSAN: data-race in ntfs_attr_find / ntfs_attr_record_resize

  write to 0xffff888100af1018 of 4 bytes by task 96 on cpu 1:
   ntfs_attr_record_resize+0xd2/0x130
   ntfs_attr_record_rm+0xad/0x530
   ntfs_delete+0x224/0x640
   ntfs_unlink+0x14d/0x280
   vfs_unlink+0x157/0x520

  read to 0xffff888100af1018 of 4 bytes by task 95 on cpu 0:
   ntfs_attr_find+0x104/0x5b0
   ntfs_attr_lookup+0x39c/0x10c0
   ntfs_read_iomap_begin_resident+0xc6/0x230
   ntfs_read_iomap_begin+0x5d/0xa0
   iomap_iter+0x2e2/0x6e0
   iomap_read_folio+0x147/0x2a0
   ntfs_read_folio+0x108/0x170
   filemap_read_folio+0x35/0x100
   filemap_fault+0x993/0x1000

  value changed: 0x00000250 -> 0x000001f0

The address is mrec + 0x18, i.e. mft_record.bytes_in_use, and the change
is the 96 bytes of one $FILE_NAME attribute being removed.

Keep base_ni->mrec_lock from the resident read iomap lookup through
iomap_end(). This protects both the attribute walk and the subsequent copy
from iomap->inline_data, which points into the MFT record. The non-resident
path is left alone: ntfs_lookup() already holds the directory inode's
mrec_lock when it reads an index folio through read_mapping_folio(), and
taking the lock in the shared wrapper deadlocks there with recursive locking
on mrec_lock. The comment above the read_mapping_folio() call in
fs/ntfs/dir.c notes the same hazard.

The seek path uses the same lookup helper but does not dereference
iomap->inline_data. Release the lock before returning from that path,
whereas the regular read path records base_ni in iomap->private and releases
the lock from its iomap_end() callback.

Tested with a reproducer that faults in a 16-byte resident file while
another thread runs link()/unlink() on it. Before: 40 KCSAN reports in
about one second. After: no reports in 180 seconds over 206,090 read
iterations and 423,540 link/unlink cycles. A PROVE_LOCKING build shows no
lockdep splat with the same reproducer running for 60 seconds.

## Which versions are affected by CVE-2026-90131?


## How do I fix CVE-2026-90131?

Apply the vendor's patch.

## Is CVE-2026-90131 being exploited?

There is no known exploitation of CVE-2026-90131 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90131 and fix it if it is affected.

What it is: CVE-2026-90131 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-90131 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-90131/ (Markdown: https://insights.sbomify.com/CVE-2026-90131/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90131
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90131
- OSV: https://osv.dev/vulnerability/CVE-2026-90131

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90131/
Summaries are generated and may contain mistakes; the official description above is the record.