# CVE-2026-72019: macsec: don't read an unset MAC header in macsec_encrypt()

> An out-of-bounds read in the Linux kernel MACsec module allows attackers to leak heap memory or cause a crash via crafted network packets.

- **Severity:** High 7.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/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:** 15 Aug 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-72019, DEBIAN-CVE-2026-72019, GHSA-593p-5684-69pq, UBUNTU-CVE-2026-72019

## What is CVE-2026-72019?

CVE-2026-72019 is a high-severity vulnerability in Linux, published on 15 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:

macsec: don't read an unset MAC header in macsec_encrypt()

macsec_encrypt() reads the Ethernet header via eth_hdr(skb)
(skb->head + skb->mac_header) to memmove() the 12 source/destination MAC
bytes forward and make room for the SecTAG.

On the AF_PACKET SOCK_RAW + PACKET_QDISC_BYPASS transmit path the skb
reaches the macsec ndo_start_xmit() with the MAC header unset, so
eth_hdr(skb) resolves to skb->head + (u16)~0 and the read is out of
bounds: a 12-byte heap over-read that is also emitted on the wire as the
frame's outer source/destination MAC. KASAN reports a slab-out-of-bounds
read in macsec_start_xmit() on 6.0; on current mainline a CONFIG_DEBUG_NET
build flags it as an unset mac header in skb_mac_header().

On the TX path the L2 header is at skb->data, so use skb_eth_hdr(), added
by commit 96cc4b69581d ("macvlan: do not assume mac_header is set in
macvlan_broadcast()") for exactly this purpose.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-72019?


## How do I fix CVE-2026-72019?

Apply the vendor's patch.

## Is CVE-2026-72019 being exploited?

There is no known exploitation of CVE-2026-72019 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72019 and fix it if it is affected.

What it is: CVE-2026-72019 is a high-severity vulnerability in Linux, published on 15 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-2026-72019 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-2026-72019/ (Markdown: https://insights.sbomify.com/CVE-2026-72019/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72019
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72019
- OSV: https://osv.dev/vulnerability/CVE-2026-72019

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72019/
Summaries are generated and may contain mistakes; the official description above is the record.