# CVE-2026-89785: fs/ntfs3: fix out-of-bounds read of INDEX_ROOT in reparse/objid init

> A local attacker with CAP_SYS_ADMIN can trigger an out-of-bounds read in the Linux kernel NTFS3 driver by mounting a crafted image, potentially causing a crash or leaking memory.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101345, BELL-CVE-2026-89785, DEBIAN-CVE-2026-89785, GHSA-683x-gqv7-78pp, UBUNTU-CVE-2026-89785

## What is CVE-2026-89785?

CVE-2026-89785 is a memory corruption vulnerability in Linux, published on 16 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:

fs/ntfs3: fix out-of-bounds read of INDEX_ROOT in reparse/objid init

ntfs_reparse_init() and ntfs_objid_init() parse the index root of the
$Extend/$Reparse and $Extend/$ObjId metafiles (the INDEX_ROOT attributes
named $R and $O). They read its type and rule fields through
resident_data(), which does not check that the resident attribute is
large enough to hold them.

mi_enum_attr() accepts a resident attribute with data_off == asize and
data_size == 0. For such an attribute placed last in its MFT record,
resident_data() returns a pointer to the end of the record_size buffer,
so reading root->type / root->rule reads past the allocation.

Use resident_data_ex(attr, sizeof(struct INDEX_ROOT)) and bail out when
it returns NULL, as ntfs_security_init() already does for $SDH / $SII.

The attribute is only parsed while mounting a crafted image, so this
needs CAP_SYS_ADMIN.

 BUG: KASAN: slab-out-of-bounds in ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306)
 Read of size 4 at addr ffff88801219dc00 by task mount
  ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306)
  ntfs_fill_super (fs/ntfs3/super.c:1604)
  get_tree_bdev_flags (fs/super.c:1703)
  vfs_get_tree (fs/super.c:1758)
  path_mount (fs/namespace.c:4131)
  __x64_sys_mount (fs/namespace.c:4360)

## Which versions are affected by CVE-2026-89785?


## How do I fix CVE-2026-89785?

Apply the vendor's patch.

## Is CVE-2026-89785 being exploited?

There is no known exploitation of CVE-2026-89785 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89785 and fix it if it is affected.

What it is: CVE-2026-89785 is a memory corruption vulnerability in Linux, published on 16 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-2026-89785 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-2026-89785/ (Markdown: https://insights.sbomify.com/CVE-2026-89785/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89785
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89785
- OSV: https://osv.dev/vulnerability/CVE-2026-89785

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89785/
Summaries are generated and may contain mistakes; the official description above is the record.