# CVE-2026-97563: smb: client: reject out-of-bounds DataOffset in CIFSSMBRead()

> A malicious SMB1 server can trigger out-of-bounds reads in the Linux kernel, leading to information disclosure or denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104279, BELL-CVE-2026-97563, DEBIAN-CVE-2026-97563, GHSA-wp4g-rrmp-2p82, UBUNTU-CVE-2026-97563

## What is CVE-2026-97563?

CVE-2026-97563 is a vulnerability in Linux, published on 25 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:

smb: client: reject out-of-bounds DataOffset in CIFSSMBRead()

The SMB1 synchronous read helper CIFSSMBRead() validates the server's
DataLength against CIFSMaxBufSize and the caller's count, but never
validates DataOffset. The copy source is formed as

	&pSMBr->hdr.Protocol + le16_to_cpu(pSMBr->DataOffset)

and memcpy()'d for DataLength bytes with no check that the
[DataOffset, DataOffset + DataLength) range lies within the response
actually received from the server.

A malicious or compromised SMB1 server can return a response carrying
an in-range DataLength and a large DataOffset, driving the source
pointer past the end of the response buffer. The memcpy() then copies
adjacent kernel heap into the caller's read buffer (information
disclosure), or reads unmapped memory and oopses (denial of service).
SMB1 is not negotiated by default; reaching this code requires an
explicit vers=1.0 mount.

Both DataOffset and the received response length recorded in
rsp_iov.iov_len are relative to the start of the SMB header, so reject
the response unless DataOffset + DataLength fits within that length,
using overflow-safe arithmetic, before forming the source pointer.
The response length has been validated by the previous patch, so the
DataOffset and DataLength fields can be read safely here.

While here, make data_length unsigned. It holds a length derived from
unsigned on-the-wire fields and is only ever compared against unsigned
quantities; print it with %u accordingly, and add __func__ to the
cifs_dbg() calls in this function.

## Which versions are affected by CVE-2026-97563?


## How do I fix CVE-2026-97563?

Apply the vendor's patch.

## Is CVE-2026-97563 being exploited?

There is no known exploitation of CVE-2026-97563 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97563 and fix it if it is affected.

What it is: CVE-2026-97563 is a vulnerability in Linux, published on 25 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-2026-97563 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-2026-97563/ (Markdown: https://insights.sbomify.com/CVE-2026-97563/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97563
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97563
- OSV: https://osv.dev/vulnerability/CVE-2026-97563

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97563/
Summaries are generated and may contain mistakes; the official description above is the record.