# CVE-2026-89786: ext4: fix out-of-bounds read in ext4_read_inline_dir()

> A local attacker can trigger an out-of-bounds read in the ext4 filesystem, potentially leaking kernel memory or causing a system crash.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101309, BELL-CVE-2026-89786, DEBIAN-CVE-2026-89786, GHSA-7xr2-rx94-5f89, UBUNTU-CVE-2026-89786

## What is CVE-2026-89786?

CVE-2026-89786 is a critical memory corruption vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ext4: fix out-of-bounds read in ext4_read_inline_dir()

ext4_read_inline_dir() can read a dirent header past the end of its inline
buffer, triggering a slab-out-of-bounds read during getdents64():

  BUG: KASAN: slab-out-of-bounds in __ext4_check_dir_entry
  Read of size 2 at addr ffff88800f3dd23c by task exploit/148
   ...
   __ext4_check_dir_entry
   ext4_read_inline_dir
   iterate_dir

The dirent payload lives in a buffer of exactly inline_size bytes:

	dir_buf = kmalloc(inline_size, GFP_NOFS);

but iteration runs in a position space extra_offset bytes larger
(extra_size = extra_offset + inline_size) so the synthetic "." and ".."
land at their block-dir offsets. A dirent is formed at "dir_buf + pos -
extra_offset", yet the ext4_check_dir_entry() length argument uses the
larger extra_size. A position whose dirent header would extend past
extra_size is therefore accepted, and the rescan loop's rec_len probe and
ext4_check_dir_entry() dereference de->rec_len before the entry is rejected.

Reject a position whose minimum-size dirent header would not fit within
extra_size before forming de, in both the rescan and main loops, and pass
inline_size rather than extra_size to ext4_check_dir_entry() so the length
check matches the physical buffer.

## Which versions are affected by CVE-2026-89786?


## How do I fix CVE-2026-89786?

Apply the vendor's patch.

## Is CVE-2026-89786 being exploited?

There is no known exploitation of CVE-2026-89786 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89786 and fix it if it is affected.

What it is: CVE-2026-89786 is a critical memory corruption vulnerability in Linux, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89786 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-2026-89786/ (Markdown: https://insights.sbomify.com/CVE-2026-89786/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89786
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89786
- OSV: https://osv.dev/vulnerability/CVE-2026-89786

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89786/
Summaries are generated and may contain mistakes; the official description above is the record.