# CVE-2026-93186: cxl/mbox: Clamp mailbox output allocation to the payload size

> A local attacker can trigger a kernel panic or denial of service by requesting an excessively large mailbox output allocation in the CXL memory driver.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102953, BELL-CVE-2026-93186, DEBIAN-CVE-2026-93186, GHSA-4xf9-vh86-48mc, UBUNTU-CVE-2026-93186

## What is CVE-2026-93186?

CVE-2026-93186 is a denial of service vulnerability in Linux, published on 17 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:

cxl/mbox: Clamp mailbox output allocation to the payload size

CXL_MEM_SEND_COMMAND bounds the user's in.size to the mailbox payload
size but leaves out.size unbounded, then cxl_mbox_cmd_ctor() calls
kvzalloc(out.size). A large out.size drives a huge allocation, above
INT_MAX it WARNs and taints, and with panic_on_warn=1 it panics.

The transport __cxl_pci_mbox_send_cmd() already clamps the response copy
to min(out.size, payload_size, device len), so the output buffer is
never written beyond payload_size. Clamp the allocation to payload_size
too, matching the RAW path.

## Which versions are affected by CVE-2026-93186?


## How do I fix CVE-2026-93186?

Apply the vendor's patch.

## Is CVE-2026-93186 being exploited?

There is no known exploitation of CVE-2026-93186 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93186 and fix it if it is affected.

What it is: CVE-2026-93186 is a denial of service vulnerability in Linux, published on 17 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-2026-93186 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-2026-93186/ (Markdown: https://insights.sbomify.com/CVE-2026-93186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93186
- OSV: https://osv.dev/vulnerability/CVE-2026-93186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93186/
Summaries are generated and may contain mistakes; the official description above is the record.