# CVE-2026-31708: smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path

> A malicious SMB server can trigger an out-of-bounds read in the Linux kernel, exposing adjacent kernel heap memory to userspace.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 1 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-85445, BELL-CVE-2026-31708, DEBIAN-CVE-2026-31708, GHSA-9grv-w29f-qpm9, ROOT-OS-DEBIAN-11-CVE-2026-31708, ROOT-OS-DEBIAN-12-CVE-2026-31708, ROOT-OS-UBUNTU-2204-CVE-2026-31708, ROOT-OS-UBUNTU-2404-CVE-2026-31708, UBUNTU-CVE-2026-31708

## What is CVE-2026-31708?

CVE-2026-31708 is a high-severity vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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

smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path

smb2_ioctl_query_info() has two response-copy branches: PASSTHRU_FSCTL
and the default QUERY_INFO path.  The QUERY_INFO branch clamps
qi.input_buffer_length to the server-reported OutputBufferLength and then
copies qi.input_buffer_length bytes from qi_rsp->Buffer to userspace, but
it never verifies that the flexible-array payload actually fits within
rsp_iov[1].iov_len.

A malicious server can return OutputBufferLength larger than the actual
QUERY_INFO response, causing copy_to_user() to walk past the response
buffer and expose adjacent kernel heap to userspace.

Guard the QUERY_INFO copy with a bounds check on the actual Buffer
payload.  Use struct_size(qi_rsp, Buffer, qi.input_buffer_length)
rather than an open-coded addition so the guard cannot overflow on
32-bit builds.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-31708?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31708?

Apply the vendor's patch.

## Is CVE-2026-31708 being exploited?

There is no known exploitation of CVE-2026-31708 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31708 and fix it if it is affected.

What it is: CVE-2026-31708 is a high-severity vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-31708 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31708/ (Markdown: https://insights.sbomify.com/CVE-2026-31708/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31708
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31708
- OSV: https://osv.dev/vulnerability/CVE-2026-31708

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31708/
Summaries are generated and may contain mistakes; the official description above is the record.