# CVE-2026-52945: Revert "wireguard: device: enable threaded NAPI"

> A race condition in the Linux kernel WireGuard driver causes permanent network stalls for specific peers under heavy load, requiring a patch to revert threaded NAPI.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-52945, DEBIAN-CVE-2026-52945, GHSA-rh26-99wm-wg2w, ROOT-OS-UBUNTU-2204-CVE-2026-52945, ROOT-OS-UBUNTU-2404-CVE-2026-52945, UBUNTU-CVE-2026-52945

## What is CVE-2026-52945?

CVE-2026-52945 is a high-severity vulnerability in Linux kernel, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

Revert "wireguard: device: enable threaded NAPI"

This reverts commit 933466fc50a8e4eb167acbd0d8ec96a078462e9c which is
commit db9ae3b6b43c79b1ba87eea849fd65efa05b4b2e upstream.

We have had three independent production user reports in combination
with Cilium utilizing WireGuard as encryption underneath that k8s Pod
E/W traffic to certain peer nodes fully stalled. The situation appears
as follows:

  - Occurs very rarely but at random times under heavy networking load.
  - Once the issue triggers the decryption side stops working completely
    for that WireGuard peer, other peers keep working fine. The stall
    happens also for newly initiated connections towards that particular
    WireGuard peer.
  - Only the decryption side is affected, never the encryption side.
  - Once it triggers, it never recovers and remains in this state,
    the CPU/mem on that node looks normal, no leak, busy loop or crash.
  - bpftrace on the affected system shows that wg_prev_queue_enqueue
    fails, thus the MAX_QUEUED_PACKETS (1024 skbs!) for the peer's
    rx_queue is reached.
  - Also, bpftrace shows that wg_packet_rx_poll for that peer is never
    called again after reaching this state for that peer. For other
    peers wg_packet_rx_poll does get called normally.
  - Commit db9ae3b ("wireguard: device: enable threaded NAPI")
    switched WireGuard to threaded NAPI by default. The default has
    not been changed for triggering the issue, neither did CPU
    hotplugging occur (i.e. 5bd8de2 ("wireguard: queueing: always
    return valid online CPU in wg_cpumask_choose_online()")).
  - The issue has been observed with stable kernels of v5.15 as well as
    v6.1. It was reported to us that v5.10 stable is working fine, and
    no report on v6.6 stable either (somewhat related discussion in [0]
    though).
  - In the WireGuard driver the only material difference between v5.10
    stable and v5.15 stable is the switch to threaded NAPI by default.

    [0] https://lore.kernel.org/netdev/CA+wXwBTT74RErDGAnj98PqS=wvdh8eM1pi4q6tTdExtjnokKqA@mail.gmail.com/

Breakdown of the problem:

  1) skbs arriving for decryption are enqueued to the peer->rx_queue in
     wg_packet_consume_data via wg_queue_enqueue_per_device_and_peer.
  2) The latter only moves the skb into the MPSC peer queue if it does
     not surpass MAX_QUEUED_PACKETS (1024) which is kept track in an
     atomic counter via wg_prev_queue_enqueue.
  3) In case enqueueing was successful, the skb is also queued up
     in the device queue, round-robin picks a next online CPU, and
     schedules the decryption worker.
  4) The wg_packet_decrypt_worker, once scheduled, picks these up
     from the queue, decrypts the packets and once done calls into
     wg_queue_enqueue_per_peer_rx.
  5) The latter updates the state to PACKET_STATE_CRYPTED on success
     and calls napi_schedule on the per peer->napi instance.
  6) NAPI then polls via wg_packet_rx_poll. wg_prev_queue_peek checks
     on the peer->rx_queue. It will wg_prev_queue_dequeue if the
     queue->peeked skb was not cached yet, or just return the latter
     otherwise. (wg_prev_queue_drop_peeked later clears the cache.)
  7) From an ordering perspective, the peer->rx_queue has skbs in order
     while the device queue with the per-CPU worker threads from a
     global ordering PoV can finish the decryption and signal the skb
     PACKET_STATE_CRYPTED out of order.
  8) A situation can be observed that the first packet coming in will
     be stuck waiting for the decryption worker to be scheduled for
     a longer time when the system is under pressure.
  9) While this is the case, the other CPUs in the meantime finish
     decryption and call into napi_schedule.
 10) Now in wg_packet_rx_poll it picks up the first in-order skb
     from the peer->rx_queue and sees that its state is still
     PACKET_STATE_UNCRYPTED. The NAPI poll routine then exits e
---truncated---

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-52945?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52945?

Apply the vendor's patch.

## Is CVE-2026-52945 being exploited?

There is no known exploitation of CVE-2026-52945 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-52945 and fix it if it is affected.

What it is: CVE-2026-52945 is a high-severity vulnerability in Linux kernel, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-52945 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-52945/ (Markdown: https://insights.sbomify.com/CVE-2026-52945/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52945
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52945
- OSV: https://osv.dev/vulnerability/CVE-2026-52945

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52945/
Summaries are generated and may contain mistakes; the official description above is the record.