CVE-2026-89562 ip6_gre: fix hardware header length for NBMA tunnels
Incorrect hardware header length calculation in Linux kernel ip6_gre NBMA tunnels can lead to network instability or denial of service.
- 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
What is CVE-2026-89562?
CVE-2026-89562 is a high-severity vulnerability in Linux, published on 11 Sep 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:
ip6_gre: fix hardware header length for NBMA tunnels
ip6gre_tnl_link_config_route() accumulates the lower device's hardware header length into dev->hard_header_len whenever header_ops is set. This is incorrect for both users of header_ops.
ip6gretap and ip6erspan have a fixed Ethernet hardware header length. For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header, the optional FOU or GUE header, and the outer IPv6 header. The lower device header is headroom needed later, not part of the tunnel device's hardware header.
Keep the lower device header in needed_headroom. Set hard_header_len to the tunnel header length only for ARPHRD_IP6GRE devices with header_ops, and leave the fixed Ethernet header length unchanged for tap and erspan devices.
Which versions are affected by CVE-2026-89562?
How do I fix CVE-2026-89562?
Apply the vendor's patch.
Is CVE-2026-89562 being exploited?
There is no known exploitation of CVE-2026-89562 in the wild and no public exploit code.
Sources
Also known as AZL-100340, BELL-CVE-2026-89562, DEBIAN-CVE-2026-89562, GHSA-672h-29w5-4fj2, UBUNTU-CVE-2026-89562.