# CVE-2026-89634: smb: client: fix ALIGN() overflow in symlink_data() error context loop

> An integer overflow in the Linux kernel SMB client allows attackers to bypass bounds checks, potentially causing infinite loops or out-of-bounds reads.

- **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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100628, BELL-CVE-2026-89634, DEBIAN-CVE-2026-89634, GHSA-959h-4fxq-gqhj, UBUNTU-CVE-2026-89634

## What is CVE-2026-89634?

CVE-2026-89634 is a critical vulnerability in Linux, published on 11 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:

smb: client: fix ALIGN() overflow in symlink_data() error context loop

The check added by commit 7d9a7f1f96cd ("smb/client: fix possible
infinite loop and oob read in symlink_data()") compared the post-ALIGN
length against the remaining buffer, but ALIGN() itself can overflow:
for ErrorDataLength near UINT32_MAX (e.g. 0xFFFFFFF9), ALIGN(x, 8)
wraps to 0, so the subsequent bounds check passes, and the loop
advances by zero bytes leaving 'p' pointing into stale data.

Fix by checking the raw ErrorDataLength against the remaining space
before applying ALIGN(), then checking again after.  Since raw_len is
bounded by the buffer, raw_len + 7 cannot overflow, so the second check
is an exact post-alignment bounds guard.

## Which versions are affected by CVE-2026-89634?


## How do I fix CVE-2026-89634?

Apply the vendor's patch.

## Is CVE-2026-89634 being exploited?

There is no known exploitation of CVE-2026-89634 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89634 and fix it if it is affected.

What it is: CVE-2026-89634 is a critical vulnerability in Linux, published on 11 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-2026-89634 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-2026-89634/ (Markdown: https://insights.sbomify.com/CVE-2026-89634/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89634
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89634
- OSV: https://osv.dev/vulnerability/CVE-2026-89634

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89634/
Summaries are generated and may contain mistakes; the official description above is the record.