# CVE-2026-98558: net: flush skb_defer_nodes in dev_cpu_dead()

> A race condition in the Linux kernel network stack can cause indefinite stalls during CPU offline events, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-109244, BELL-CVE-2026-98558, DEBIAN-CVE-2026-98558, GHSA-prw3-7248-3734, UBUNTU-CVE-2026-98558

## What is CVE-2026-98558?

CVE-2026-98558 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net: flush skb_defer_nodes in dev_cpu_dead()

When a CPU goes offline, dev_cpu_dead() drains its softnet queues
(completion_queue, output_queue, poll_list, process_queue, and
input_pkt_queue), but leaves net_hotdata.skb_defer_nodes untouched.

If oldcpu goes offline while holding pending skbs in its
skb_defer_nodes lists (e.g. below the sysctl_skb_defer_max >> 1 IPI
threshold, or if the IPI races with CPU teardown), those skbs remain
stranded until oldcpu is brought back online. If any of these skbs
hold page_pool fragments, page_pool_destroy() will stall indefinitely
waiting for inflight pages to be returned when a netdev or driver is
torn down while oldcpu is offline.

Additionally, if smp_call_function_single_async() fails in
kick_defer_list_purge() because the target CPU went offline, reset
defer_ipi_scheduled to 0 so future IPI kicks are not blocked when the
CPU comes back online.

Also, if oldcpu was the last online CPU on its NUMA node, drain that
node's slot across all CPUs so no skbs deferred from that node remain
stranded on idle remote CPUs (or if the node itself is subsequently
offlined).

Finally, in skb_attempt_defer_free(), re-check cpu_online(cpu) and
whether the caller migrated CPUs after llist_add(), flushing the node
list if so, to close the preemption TOCTOU race against CPU/node
teardown.

## Which versions are affected by CVE-2026-98558?


## How do I fix CVE-2026-98558?

Apply the vendor's patch.

## Is CVE-2026-98558 being exploited?

There is no known exploitation of CVE-2026-98558 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98558 and fix it if it is affected.

What it is: CVE-2026-98558 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98558 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98558/ (Markdown: https://insights.sbomify.com/CVE-2026-98558/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98558
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98558
- OSV: https://osv.dev/vulnerability/CVE-2026-98558

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98558/
Summaries are generated and may contain mistakes; the official description above is the record.