CVE-2026-74743 macvlan: inherit needed_headroom and needed_tailroom from lowerdev
A Linux kernel macvlan bug causes use-after-free crashes when lower devices require extra headroom, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74743?
CVE-2026-74743 is a critical use after free vulnerability in Linux, published on 26 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-74743?
How do I fix CVE-2026-74743?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-74743 being exploited?
There is no known exploitation of CVE-2026-74743 in the wild and no public exploit code.
Sources
Also known as AZL-97782, BELL-CVE-2026-74743, DEBIAN-CVE-2026-74743, GHSA-5qfp-9h7g-rcpm, UBUNTU-CVE-2026-74743.