# CVE-2026-31535: smb: client: make use of smbdirect_socket.recv_io.credits.available

> A race condition in the Linux kernel SMB client credit management can lead to denial of service by granting non-existent credits to peers.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Apr 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31535, DEBIAN-CVE-2026-31535, GHSA-4w64-3hfc-pgqc, UBUNTU-CVE-2026-31535

## What is CVE-2026-31535?

CVE-2026-31535 is a medium-severity vulnerability in Linux kernel, published on 24 Apr 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: make use of smbdirect_socket.recv_io.credits.available

The logic off managing recv credits by counting posted recv_io and
granted credits is racy.

That's because the peer might already consumed a credit,
but between receiving the incoming recv at the hardware
and processing the completion in the 'recv_done' functions
we likely have a window where we grant credits, which
don't really exist.

So we better have a decicated counter for the
available credits, which will be incremented
when we posted new recv buffers and drained when
we grant the credits to the peer.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-31535?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31535?

Apply the vendor's patch.

## Is CVE-2026-31535 being exploited?

There is no known exploitation of CVE-2026-31535 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-2026-31535 and fix it if it is affected.

What it is: CVE-2026-31535 is a medium-severity vulnerability in Linux kernel, published on 24 Apr 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-2026-31535 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-2026-31535/ (Markdown: https://insights.sbomify.com/CVE-2026-31535/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31535
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31535
- OSV: https://osv.dev/vulnerability/CVE-2026-31535

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31535/
Summaries are generated and may contain mistakes; the official description above is the record.