# CVE-2026-90191: mailbox: riscv-sbi-mpxy: validate RPMI notification lengths

> A missing length validation in the Linux kernel RISC-V SBI mailbox driver allows memory corruption via crafted RPMI notifications, potentially leading to code execution or crashes.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-90191, DEBIAN-CVE-2026-90191, GHSA-m5w6-3p2w-2mgg, UBUNTU-CVE-2026-90191

## What is CVE-2026-90191?

CVE-2026-90191 is a high-severity memory corruption 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:

mailbox: riscv-sbi-mpxy: validate RPMI notification lengths

The SBI return value controls how many bytes are copied from shared
memory into the RPMI notification buffer. It is not validated against
the negotiated shared-memory size before that copy. The event walker
also uses a reversed loop condition and can inspect a short event record.

Validate the complete notification length before copying it, iterate only
while a full event header remains, and stop when a declared event payload
extends beyond the copied notification data.

## Which versions are affected by CVE-2026-90191?


## How do I fix CVE-2026-90191?

Apply the vendor's patch.

## Is CVE-2026-90191 being exploited?

There is no known exploitation of CVE-2026-90191 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90191 and fix it if it is affected.

What it is: CVE-2026-90191 is a high-severity memory corruption 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-2026-90191 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-2026-90191/ (Markdown: https://insights.sbomify.com/CVE-2026-90191/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90191
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90191
- OSV: https://osv.dev/vulnerability/CVE-2026-90191

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90191/
Summaries are generated and may contain mistakes; the official description above is the record.