# CVE-2026-72196: fs/ntfs3: bound copy_lcns dp->page_lcns[] index in analysis pass

> A missing bounds check in the Linux kernel NTFS3 driver allows out-of-bounds writes during log replay, potentially leading to memory corruption or system crashes.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/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:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72196, DEBIAN-CVE-2026-72196, GHSA-7v7p-59m6-6h9x, UBUNTU-CVE-2026-72196

## What is CVE-2026-72196?

CVE-2026-72196 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 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:

fs/ntfs3: bound copy_lcns dp->page_lcns[] index in analysis pass

In log_replay()'s analysis pass, after find_dp() returns a
valid DIR_PAGE_ENTRY for the (target_attr, target_vcn) tuple,
the copy_lcns block walks lrh->lcns_follow further entries:

	t16 = le16_to_cpu(lrh->lcns_follow);
	for (i = 0; i < t16; i++) {
	    size_t j = (size_t)(le64_to_cpu(lrh->target_vcn) -
	                        le64_to_cpu(dp->vcn));
	    dp->page_lcns[j + i] = lrh->page_lcns[i];
	}

find_dp() only validates that target_vcn falls within
[dp->vcn, dp->vcn + dp->lcns_follow), i.e., that the FIRST
cluster is covered.  The walk through the further entries is
not bounded against dp->lcns_follow.  For a malformed LRH
where target_vcn = dp->vcn + dp->lcns_follow - 1 and
lrh->lcns_follow > 1, the i > 0 writes overflow the dp's
allocated page_lcns[] array.

Add the missing j + lrh->lcns_follow <= dp->lcns_follow guard.

Reproduced under UML+KASAN on mainline 8d90b09e6741 as a
slab-out-of-bounds write of size 8 from log_replay+0x68d4 on
the mount path.

This is distinct from Pavitra Jha's 2026-05-02 patch
("fs/ntfs3: validate lcns_follow in log_replay conversion",
<20260502154252.164586-1-jhapavitra98@gmail.com>) which
addresses the separate version-0 dirty-page-table conversion
path's memmove(&dp->vcn, ...) call.  The two fixes are
complementary; both should land.

[almaz.alexandrovich@paragon-software.com: clang-formatted the changes,
fixed conflicts]

## Which versions are affected by CVE-2026-72196?


## How do I fix CVE-2026-72196?

Apply the vendor's patch.

## Is CVE-2026-72196 being exploited?

There is no known exploitation of CVE-2026-72196 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72196 and fix it if it is affected.

What it is: CVE-2026-72196 is a high-severity memory corruption vulnerability in Linux, published on 15 Aug 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-2026-72196 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-2026-72196/ (Markdown: https://insights.sbomify.com/CVE-2026-72196/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72196
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72196
- OSV: https://osv.dev/vulnerability/CVE-2026-72196

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72196/
Summaries are generated and may contain mistakes; the official description above is the record.