CVE-2026-98554 vlan: ensure sufficient headroom in vlan_dev_hard_header()
A flaw in the Linux kernel VLAN handling can cause a system crash via skb_under_panic when insufficient headroom is reserved, 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-2026-98554?
CVE-2026-98554 is a denial of service vulnerability in Linux, published on 18 Oct 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:
vlan: ensure sufficient headroom in vlan_dev_hard_header()
Callers that only reserve ETH_HLEN or less (such as llc_alloc_frame()), or skbs allocated before dynamic device/headroom changes (e.g. toggling VLAN_FLAG_REORDER_HDR or bonding/team switching slaves), can reach vlan_dev_hard_header() with insufficient headroom and trigger skb_under_panic().
Use skb_cow_head() in vlan_dev_hard_header() when VLAN_FLAG_REORDER_HDR is not set to ensure sufficient headroom for the VLAN header(s) and the underlying device hard header.
Use READ_ONCE() to read dev->hard_header_len and dev->needed_headroom as they can be updated concurrently under RTNL (e.g. in vlan_transfer_features()) while vlan_dev_hard_header() runs locklessly on the transmit path. Also avoid LL_RESERVED_SPACE(dev) here so that the extra HH_DATA_MOD alignment padding does not trigger unnecessary pskb_expand_head() reallocations on inner stacked VLAN devices after the outer VLAN header has been pushed.
Which versions are affected by CVE-2026-98554?
How do I fix CVE-2026-98554?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-98554 being exploited?
There is no known exploitation of CVE-2026-98554 in the wild and no public exploit code.
Sources
Also known as AZL-108854, BELL-CVE-2026-98554, DEBIAN-CVE-2026-98554, GHSA-xh57-3wrj-366f, UBUNTU-CVE-2026-98554.