# CVE-2026-68338: net/packet: avoid fanout hook re-registration after unregister

> A race condition in the Linux kernel packet socket implementation can lead to invalid hook re-registration, potentially causing system instability or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 10 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-68338, DEBIAN-CVE-2026-68338, GHSA-xrw5-g7cv-c5p3, UBUNTU-CVE-2026-68338

## What is CVE-2026-68338?

CVE-2026-68338 is a high-severity vulnerability in Linux, published on 10 Aug 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/packet: avoid fanout hook re-registration after unregister

packet_set_ring() temporarily detaches a socket from packet delivery while
reconfiguring its ring. It records the previous running state, clears
po->num, unregisters the protocol hook when needed, drops po->bind_lock,
and later restores po->num and re-registers the hook from the saved
was_running value.

That unlocked window can race with NETDEV_UNREGISTER. The notifier can
observe the socket as not running, skip __unregister_prot_hook(), and
invalidate the per-socket binding by setting po->ifindex to -1 and clearing
po->prot_hook.dev. A one-member fanout group can still retain its shared
fanout hook device pointer. When packet_set_ring() resumes, re-registering
solely from the stale was_running state can re-add the fanout hook after
the device has been unregistered.

Treat po->ifindex == -1 as an invalidated binding after reacquiring
po->bind_lock. This is distinct from ifindex 0, the normal
unbound/wildcard state: ifindex -1 marks an existing device binding that
was invalidated when the device was unregistered. Restore po->num as
before, but do not re-register the hook if device unregister already
detached the socket.

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

## Which versions are affected by CVE-2026-68338?


## How do I fix CVE-2026-68338?

Apply the vendor's patch.

## Is CVE-2026-68338 being exploited?

There is no known exploitation of CVE-2026-68338 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68338 and fix it if it is affected.

What it is: CVE-2026-68338 is a high-severity vulnerability in Linux, published on 10 Aug 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-2026-68338 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-2026-68338/ (Markdown: https://insights.sbomify.com/CVE-2026-68338/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68338
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68338
- OSV: https://osv.dev/vulnerability/CVE-2026-68338

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68338/
Summaries are generated and may contain mistakes; the official description above is the record.