# CVE-2026-89726: lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

> An off-by-one out-of-bounds read in the Linux kernel's ucs2_strnlen function allows attackers to read memory past buffer limits, potentially causing crashes or information leaks.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Not stated
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100106, BELL-CVE-2026-89726, DEBIAN-CVE-2026-89726, GHSA-rfcj-g8r9-q3mj, UBUNTU-CVE-2026-89726

## What is CVE-2026-89726?

CVE-2026-89726 is a memory corruption vulnerability in Linux, published on 11 Sep 2026. 

### Official description

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

lib/ucs2_string.c: fix out-of-bounds read in ucs2_strnlen()

Patch series "lib/ucs2_string.c: fix out-of-bounds read in
ucs2_strnlen()", v2.

This series fixes an off-by-one out-of-bounds read in ucs2_strnlen().

The first patch is the real fix, the second patch comes as a bonus and
fixes the code indentation.

This patch (of 2):

ucs2_strnlen() checks the current character before checking whether the
caller-provided maximum length has been reached.  If the input is not
NUL-terminated within that bound, the loop can read one ucs2_char_t past
the limit.

Test the length before dereferencing to prevent an off-by-one
out-of-bounds read.

## Which versions are affected by CVE-2026-89726?


## How do I fix CVE-2026-89726?

Apply the vendor's patch.

## Is CVE-2026-89726 being exploited?

There is no known exploitation of CVE-2026-89726 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89726 and fix it if it is affected.

What it is: CVE-2026-89726 is a memory corruption vulnerability in Linux, published on 11 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-89726 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-2026-89726/ (Markdown: https://insights.sbomify.com/CVE-2026-89726/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89726
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89726
- OSV: https://osv.dev/vulnerability/CVE-2026-89726

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89726/
Summaries are generated and may contain mistakes; the official description above is the record.