# CVE-2026-89632: smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()

> A malicious SMB server can cause a kernel crash by sending a small response, leading to a use-before-check vulnerability in the Linux kernel SMB client.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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:** 21 Oct 2026
- **Also known as:** AZL-100757, BELL-CVE-2026-89632, DEBIAN-CVE-2026-89632, GHSA-j6wx-7c3w-595c, UBUNTU-CVE-2026-89632

## What is CVE-2026-89632?

CVE-2026-89632 is a high-severity 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 use-before-check of ReparseDataLength in reparse_buf_ptr()

reparse_buf_ptr() reads buf->ReparseDataLength before checking that
count covers the full fixed header:

    buf = (struct reparse_data_buffer *)((u8 *)io + off);
    len = sizeof(*buf);                          /* 8 bytes */
    rdlen = le16_to_cpu(buf->ReparseDataLength); /* offset 4, 2 bytes */

    if (count < len || count < rdlen + len)      /* check comes after */

struct reparse_data_buffer has ReparseDataLength at offset 4.  If a
server returns OutputCount < 6, the read at offset 4-5 reaches past
the end of the received data.  The off+count bounds against iov_len
were already validated, but that does not protect against count being
smaller than sizeof(*buf).

Split the check: verify count >= sizeof(*buf) before reading
ReparseDataLength, then verify count covers the data region.

## Which versions are affected by CVE-2026-89632?


## How do I fix CVE-2026-89632?

Apply the vendor's patch.

## Is CVE-2026-89632 being exploited?

There is no known exploitation of CVE-2026-89632 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89632 and fix it if it is affected.

What it is: CVE-2026-89632 is a high-severity 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-2026-89632 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-2026-89632/ (Markdown: https://insights.sbomify.com/CVE-2026-89632/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89632
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89632
- OSV: https://osv.dev/vulnerability/CVE-2026-89632

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89632/
Summaries are generated and may contain mistakes; the official description above is the record.