# CVE-2026-31691: igb: remove napi_synchronize() in igb_down()

> An abrupt termination of an AF_XDP application causes the igb network driver to hang indefinitely, resulting in a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Apr 2026
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2026-31691, DEBIAN-CVE-2026-31691, GHSA-3mf8-6wc5-2f9c, UBUNTU-CVE-2026-31691

## What is CVE-2026-31691?

CVE-2026-31691 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Apr 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:

igb: remove napi_synchronize() in igb_down()

When an AF_XDP zero-copy application terminates abruptly (e.g., kill -9),
the XSK buffer pool is destroyed but NAPI polling continues.
igb_clean_rx_irq_zc() repeatedly returns the full budget, preventing
napi_complete_done() from clearing NAPI_STATE_SCHED.

igb_down() calls napi_synchronize() before napi_disable() for each queue
vector. napi_synchronize() spins waiting for NAPI_STATE_SCHED to clear,
which never happens. igb_down() blocks indefinitely, the TX watchdog
fires, and the TX queue remains permanently stalled.

napi_disable() already handles this correctly: it sets NAPI_STATE_DISABLE.
After a full-budget poll, __napi_poll() checks napi_disable_pending(). If
set, it forces completion and clears NAPI_STATE_SCHED, breaking the loop
that napi_synchronize() cannot.

napi_synchronize() was added in commit 41f149a285da ("igb: Fix possible
panic caused by Rx traffic arrival while interface is down").
napi_disable() provides stronger guarantees: it prevents further
scheduling and waits for any active poll to exit.
Other Intel drivers (ixgbe, ice, i40e) use napi_disable() without a
preceding napi_synchronize() in their down paths.

Remove redundant napi_synchronize() call and reorder napi_disable()
before igb_set_queue_napi() so the queue-to-NAPI mapping is only
cleared after polling has fully stopped.

## Which versions are affected by CVE-2026-31691?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31691?

Apply the vendor's patch.

## Is CVE-2026-31691 being exploited?

There is no known exploitation of CVE-2026-31691 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-2026-31691 and fix it if it is affected.

What it is: CVE-2026-31691 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Apr 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-2026-31691 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-2026-31691/ (Markdown: https://insights.sbomify.com/CVE-2026-31691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31691
- OSV: https://osv.dev/vulnerability/CVE-2026-31691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31691/
Summaries are generated and may contain mistakes; the official description above is the record.