# CVE-2026-80742: af_packet: Don't send zero-byte data in tpacket_snd().

> A local attacker can trigger a kernel warning and potential denial of service by sending zero-byte packets via TPACKET ring buffers.

- **Severity:** Not scored
- **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:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** AZL-99036, BELL-CVE-2026-80742, DEBIAN-CVE-2026-80742, GHSA-66qw-vmh2-j2c2, UBUNTU-CVE-2026-80742

## What is CVE-2026-80742?

CVE-2026-80742 is a denial of service vulnerability in Linux, published on 3 Sep 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:

af_packet: Don't send zero-byte data in tpacket_snd().

syzbot reported a WARNING in __dev_queue_xmit() triggered via tpacket_snd():

skb_assert_len
WARNING: at include/linux/skbuff.h:2753 skb_assert_len
WARNING: at __dev_queue_xmit+0x21bc/0x4970 net/core/dev.c:4781

Call Trace:
 <TASK>
 dev_queue_xmit include/linux/netdevice.h:3448 [inline]
 packet_xmit+0x243/0x310 net/packet/af_packet.c:276
 tpacket_snd net/packet/af_packet.c:2907 [inline]
 packet_sendmsg+0x28d6/0x4eb0 net/packet/af_packet.c:3134

When sending 0-byte packets via TPACKET ring buffer on devices with no
hard header (e.g. dev->hard_header_len == 0), tpacket_fill_skb()
populates an skb with skb->len == 0 and returns 0. tpacket_snd() then
forwards this empty skb to packet_xmit(), causing __dev_queue_xmit() to
hit skb_assert_len(skb).

Similar checks exist in packet_snd() via commit dc633700f00f
("net/af_packet: check len when min_header_len equals to 0") and in
packet_sendmsg_spkt() via commit 6a341729fb31 ("af_packet: Don't send
zero-byte data in packet_sendmsg_spkt().").

Return -EINVAL in tpacket_fill_skb() when skb->len is zero to reject
zero-length packets in tpacket_snd().

## Which versions are affected by CVE-2026-80742?


## How do I fix CVE-2026-80742?

Apply the vendor's patch.

## Is CVE-2026-80742 being exploited?

There is no known exploitation of CVE-2026-80742 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80742 and fix it if it is affected.

What it is: CVE-2026-80742 is a denial of service vulnerability in Linux, published on 3 Sep 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-2026-80742 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-2026-80742/ (Markdown: https://insights.sbomify.com/CVE-2026-80742/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80742
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80742
- OSV: https://osv.dev/vulnerability/CVE-2026-80742

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80742/
Summaries are generated and may contain mistakes; the official description above is the record.