# CVE-2026-43185: ksmbd: fix signededness bug in smb_direct_prepare_negotiation()

> A signedness bug in the Linux kernel's ksmbd module allows attackers to trigger a heap buffer overflow via crafted SMB messages, potentially leading to code execution.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 6 May 2026
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2026-43185, DEBIAN-CVE-2026-43185, GHSA-vcg7-gx5w-x44c, ROOT-OS-DEBIAN-12-CVE-2026-43185, ROOT-OS-DEBIAN-13-CVE-2026-43185, ROOT-OS-UBUNTU-2204-CVE-2026-43185, ROOT-OS-UBUNTU-2404-CVE-2026-43185, UBUNTU-CVE-2026-43185

## What is CVE-2026-43185?

CVE-2026-43185 is a critical vulnerability in Linux kernel, published on 6 May 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:

ksmbd: fix signededness bug in smb_direct_prepare_negotiation()

smb_direct_prepare_negotiation() casts an unsigned __u32 value
from sp->max_recv_size and req->preferred_send_size to a signed
int before computing min_t(int, ...). A maliciously provided
preferred_send_size of 0x80000000 will return as smaller than
max_recv_size, and then be used to set the maximum allowed
alowed receive size for the next message.

By sending a second message with a large value (>1420 bytes)
the attacker can then achieve a heap buffer overflow.

This fix replaces min_t(int, ...) with min_t(u32)

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-43185?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43185?

Apply the vendor's patch.

## Is CVE-2026-43185 being exploited?

There is no known exploitation of CVE-2026-43185 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-2026-43185 and fix it if it is affected.

What it is: CVE-2026-43185 is a critical vulnerability in Linux kernel, published on 6 May 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-2026-43185 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-2026-43185/ (Markdown: https://insights.sbomify.com/CVE-2026-43185/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43185
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43185
- OSV: https://osv.dev/vulnerability/CVE-2026-43185

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43185/
Summaries are generated and may contain mistakes; the official description above is the record.