# CVE-2026-90199: fs/ntfs3: reject out-of-range evcn in mi_enum_attr()

> A malformed NTFS3 disk image can trigger an integer overflow in the kernel, leading to a denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102422, BELL-CVE-2026-90199, DEBIAN-CVE-2026-90199, GHSA-6r4v-32r5-fpv2, UBUNTU-CVE-2026-90199

## What is CVE-2026-90199?

CVE-2026-90199 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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

fs/ntfs3: reject out-of-range evcn in mi_enum_attr()

In mi_enum_attr(), the start/end VCN validation for non-resident
attributes is:

	if (svcn > evcn + 1) goto out;

When evcn is U64_MAX the "evcn + 1" expression wraps to 0 and any svcn
passes the check. For evcn values close to U64_MAX (but not equal to it)
the right-hand side is still a meaningless near-wrap upper bound, so a
malformed on-disk attribute with svcn == 0 and evcn near U64_MAX can pass
mi_enum_attr() unrejected.

VCN (virtual cluster number) is a cluster index, so any valid evcn is
bounded by the volume's total cluster count, which ntfs3 holds in
sbi->used.bitmap.nbits (set up in ntfs_init_from_boot() before any caller
of mi_enum_attr() runs). Reject evcn values that fall outside this range.

However, an empty non-resident attribute (no allocated clusters) is
legitimately encoded with svcn == 0 and evcn == -1 (U64_MAX), e.g. via
attr->nres.evcn = cpu_to_le64((u64)vcn - 1) with vcn == 0. That sentinel
must keep passing, so exclude evcn == U64_MAX from the range check. The
existing "svcn > evcn + 1" test still tolerates the sentinel ("0 > 0" is
false) and continues to require svcn == 0 for it, while the range check
rejects every other out-of-range evcn and thereby also defuses the
"evcn + 1" wraparound.

svcn does not need its own bound: once evcn < nbits, "svcn > evcn + 1"
implies svcn <= nbits.

[almaz.alexandrovich@paragon-software.com: fixed evcn check]

## Which versions are affected by CVE-2026-90199?


## How do I fix CVE-2026-90199?

Apply the vendor's patch.

## Is CVE-2026-90199 being exploited?

There is no known exploitation of CVE-2026-90199 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90199 and fix it if it is affected.

What it is: CVE-2026-90199 is a high-severity vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-90199 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-2026-90199/ (Markdown: https://insights.sbomify.com/CVE-2026-90199/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90199
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90199
- OSV: https://osv.dev/vulnerability/CVE-2026-90199

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90199/
Summaries are generated and may contain mistakes; the official description above is the record.